LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


The  D.  Van  Nostrand  Company 

intend  this  book  to  be  sold  to  the  Public 
at  the  advertised  price,  and  supply  it  to 
the  Trade  on  terms  which  will  not  allow 
of  reduction. 


Westminster"  Series 


THE    RAILWAY    LOCOMOTIVE 


THE     RAILWAY 
LOCOMOTIVE 


WHAT  IT  IS  AND  WHY 
IT     IS     WHAT     IT     IS 

BY 

VAUGHAN    PENDRED,  M.Inst.Mech.E.  M.I.  &  S.Inst. 
(I 


NEW    YORK 

D.   VAN  NOSTRAND   COMPANY 

23    MURRAY   AND    27    WARREN    STREETS 
1908 


CONTENTS 


SECTION   I 


THE    LOCOMOTIVE    ENGINE   AS   A    VEHICLE 


CHAP. 

PAGE 

I. 

FRAMES            

1 

II. 

BOGIES              

15 

III. 

THE   ACTION   OF   THE   BOGIE.     -      . 

.27 

IV. 

CENTRE    OF   GRAVITY      . 

33 

V. 

WHEELS             

40 

VI. 

WHEEL   AND   RAIL 

54 

VII. 

\DHESIOX 

58 

VIII. 

PROPULSION   

66 

IX. 

COUNTER-BALANCING 

73 

SECTION   II 

THE   LOCOMOTIVE   AS  A   STEAM   GENERATOR 

X.  THE   BOILER 

XI.  THE   CONSTRUCTION   OF   THE   BOILER       . 

XII.  STAY   BOLTS 

XIII.  THE   FIRE-BOX 

XIV.  THE   DESIGN   OF   BOILERS 

XV.  COMBUSTION 

XVI.  FUEL 

XVII.  THE   FRONT   END 

XVIII.  THE    BLAST   PIPE 

XIX.  STEAM 

XX.  WATER 

XXI.  PRIMING 


84 
91 
97 
102 
114 
121 
127 
136 
144 
152 
158 
162 


179757 


VI 


CONTENTS 


CHAP. 

XXII. 
XXIII. 
XXIV. 

XXV. 


THE   QUALITY   OF   STEAM 
SUPERHEATING 
BOILER  FITTINGS   . 
THE   INJECTOR 


PAGE 

169 

171 
180 

187 


SECTION   III 

THE   LOCOMOTIVE   AS   A    STEAM   ENGINE 

XXVI.  CYLINDERS   AND   VALVES         .  . 

XXVII.  FRICTION          .  .  .  . 

XXVIII.  VALVE   GEAR 

XXIX.  EXPANSION 

XXX.  THE   STEPHENSON   LINK  MOTION    . 

xxxi.  WALSCHAERT'S  AND  JOY'S  GEARS 

XXXII.  SLIDE   VALVES          .  .  .  . 

XXXIII.  COMPOUNDING          .  .  .  .  .  . 

XXXIV.  PISTON  VALVES       .  .  .  .  .  . 

XXXV.  THE   INDICATOR       .  .  .  . 

XXXVI.  TENDERS  .  . 

XXXVII.  TANK   ENGINES        .  .  .  .  .  .' 

XXXVIII.  LUBRICATION        >     .  .  .  .  .  . 

XXXIX.  BRAKES  .  .  .  .  . 

XL.  THE   RUNNING   SHED       . 

XLI.  THE   WORK   OF   THE   LOCOMOTIVE  . 


198 

209 
213 
217 
223 
230 
236 
239 
246 
250 
263 
271 
282 
285 
288 
294 


STANDARD   WORKS   ON   THE   LOCOMOTIVE   ENGINE  . 
INDEX 


305 

307 


LIST    OF    ILLUSTRATIONS 

FIG.  PAGE 

1.  STEPHENSON'S  INSIDE  AXLE  BOX 5 

2.  STEPHENSON'S  STANDARD  LOCOMOTIVE,  1838        .        .        .        .7 
3 — 16.     THE  DEVELOPMENT  OF  THE  BAR  FRAME        ....  9 

17.  AXLE   BOX 11 

18.  COMPENSATING   LEVER 12 

19.  BISSELL   BOGIE 15 

20 — 21.      GREAT   NORTHERN   SWING   LINK   BOGIE 16 

22.  FLANGING   PRESS 18 

23.  OPEN   END   BOGIE      .            . 19 

24.  CLOSED   END    BOGIE 19 

25.  STANDARD   BOGIE,    GREAT   EASTERN   RAILWAY           ....  20 

26.  STANDARD    BOGIE,    GREAT   EASTERN   RAILWAY           ....  21 

27.  DETAILS   BOGIE,    GREAT   EASTERN   RAILWAY 21 

28.  SWING   LINK   BOGIE,    GREAT   WESTERN   RAILWAY     .  .  .  .22 

29.  TRAVERSING      LEADING      AXLE,      LANCASHIRE      AND      YORKSHIRE 

RAILWAY 24 

30.  MR.  BALDRY'S  RULE  FOR  FINDING  THE  CENTRE  FROM  WHICH  TO 

STRIKE   THE   CURVE   OF   A   RADIAL   AXLE   BOX      .  ...  .25 

31.  CENTRIFUGAL  EFFORT 34 

32.  TIRE- ROLLING  MILL 41 

33.  TIRE  SECTIONS,  LANCASHIRE  AND  YORKSHIRE  RAILWAY      .        .  46 

34.  STANDARD  TIRE  AND  RAIL,  GREAT  EASTERN  RAILWAY        .        .  47 

35.  ADAMS'  ELASTIC  WHEEL 54 

36.  CENTRIFUGAL  COUPLES 75 

37.  RIGG'S  DIAGRAM 77 

38.  WIRE  TEST  FOR  HAMMER  BLOW 81 

39.  SECTIONAL  DIAGRAM  OF  BOILER 85 

40.  RADIAL  STRESS 91 

41 — 44.    EXPLODED  BOILER 100 

45.  GIRDER    STAY 102 

46.  BELPAIRE   BOILER,    "STAR"    CLASS,    GREAT   WESTERN   RAILWAY     .  104 

47.  FIRE   HOLE 107 

48.  EXPANSION   SLIDE 114 

49.  DRUMMOND'S  WATER  TUBE  FIRE-BOX 118 

50.  SMOKE-BOX,  LONDON  AND  SOUTH  WESTERN  RAILWAY  .        .        .  140 

51.  SMOKE- BOX,  SOUTH  EASTERN  AND  CHATHAM  RAILWAY  141 


viii  LIST   OF   ILLUSTRATIONS. 

FIG.  PAGE 

52.  SMOKE-BOX,    SOUTH  EASTERN   AND    CHATHAM   RAILWAY  .  .       142 

53.  STANDARD   FRONT   END    . 149 

54 — 55.      BALDWIN   SMOKE-BOX 150 

56.  HEAT  PEG 153 

57.  THE   PEABODY   CALORIMETER 166 

58—60.      THE   SCHMIDT    SUPERHEATER 175 

61.  AMERICAN  THROTTLE  VALVE 180 

62.  THROTTLE  VALVE  DETAILS .181 

63.  SAFETY  VALVE 183 

64.  RAMSBOTTOM'S  SAFETY  VALVE       .        .        .        .        .        .        .184 

65.  SECTION   OF   INJECTOR 191 

66.  SELF- STARTING   INJECTOR 194 

67.  SLIDE   VALVE 200 

68.  CYLINDER  WEAR 202 

69.  ACTION   OF   CONNECTING   ROD 204 

70.  JOY'S    VALVE   GEAR 205 

71.  CROSS-HEAD,    GREAT   EASTERN   RAILWAY 207 

72.  GAB   GEAR 214 

73.  STEPHENSON'S  LINK  MOTION 216 

74.  EXPANSION  CURVE 218 

75.  ANGULAR  ADVANCE 223 

76 — 78.    WAINWRIGHT'S  REVERSING  GEAR 226—228 

79.  WALSCHAERT'S  GEAR 232 

80.  JOY'S  GEAR     .        .         ...        .  .        .         .        .  233 

81.  SMITH'S  PISTON  VALVE 248 

82.  THOMPSON  INDICATOR  WITH  OPEN  SPRING 251 

83.  INDICATOR  DIAGRAMS 255 

84.  PICK-UP  APPARATUS,  LONDON  AND  NORTH  WESTERN  RAILWAY    .  265 

85.  FEED  WATER-HEATER,  LONDON  AND  SOUTH-WESTERN  RAILWAY.  269 

COLLISION  AT   BINA,    GREAT   INDIAN  PENINSULA   RAILWAY     .  .      272 

86 — 87.      FINDING  THE   CENTRE  OF  GRAVITY   OF  A   TANK   ENGINE        274 — 275 

88 — 89.      DERAILMENTS 278 — 279 

90.      RAMSBOTTOM   GRAVITY   LUBRICATOR 283 

91—93.      TRACTOMETER  DIAGRAMS 298,  299 

94.    IVATT'S  SPEED  DIAGRAM  301 


INTRODUCTION 

THE  literature  of  the  railway  locomotive  engine  is  already  so 
copious  that  I  think  some  explanation  of  how  this  book  came  to 
be  written  is  desirable. 

It  forms  one  of  a  series  of  volumes,  the  idea  of  publishing 
which  originated  with  Messrs.  Archibald  Constable  &  Co.  In 
the  present  day  specialisation  is  universal,  and  in  no  profession 
does  it  prevail  more  than  in  that  of  engineering.  This  will  not 
appear  remarkable  when  we  recognise  the  enormous  range  of 
subjects  with  which  the  engineer  has  to  deal. 

The  "Westminster"  series  is  intended  in  a  sense  to  bridge 
over  the  gaps  left  by  specialisation.  Thus  the  marine  engineer 
may  have  but  a  very  slight  knowledge  of  electrical  engineering, 
and  the  civil  engineer  may  be  comparatively  ignorant  concerning 
the  locomotives  which  run  on  the  railways  which  he  makes.  But 
engineers  should  have — the  younger  members  of  the  profession  in 
particular  need  to  have — a  great  deal  of  information  in  common, 
and  all  perfectly  understand  technical  language. 

Speaking  then  of  my  own  work,  I  may  say  that  I  hope  engineers 
in  any  branch  of  the  profession  who  may  read  this  book  will  find 
in  it  information  which  they  did  not  possess  before.  The 
books  which  have  hitherto  been  written  about  the  locomotive 
engine  are  all  either  strictly  specialised  or  very  "  popular."  None 
of  them  go  far  into  the  life  of  the  locomotive  engine.  The 
technical  treatise  deals  with  the  locomotive  almost  altogether  as 
a  machine.  Its  parts  are  described,  bat  the  reasons  why  they 
assume  particular  shapes,  and  why  one  shape  is  better  or  worse 
than  another  are  not  dwelt  upon,  and  nothing  is  said  about  the 
daily  life  of  the  engine.  To  use  a  metaphor,  the  locomotive  is 
handled  by  its  authors  anatomically,  not  physiologically. 

I  have  in  this  volume  attempted,  I  hope  with  some  success,  to 


x  INTRODUCTION 

break  new  ground.  Of  the  history  of  the  locomotive  I  have 
written  next  to  nothing.  I  have  endeavoured  to  describe  the 
modern  locomotive,  using  the  words  in  the  generic  sense,  and  to 
explain  why  it  is  what  it  is. 

That  I  have  left  much  unsaid  that  might  have  been  said 
with  advantage  is  a  very  evident  proposition.  My  excuse  lies  in 
the  dimensions  of  this  book,  and  the  facfc  that  it  is  not  intended 
to  be  in  any  sense  or  way  a  complete  treatise  on  railway 
locomotives.  My  purpose  has  been  to  make  the  locomotive 
intelligible ;  to  show  what  it  means  ;  the  mechanical  and  the 
physical  phenomena  on  which  it  depends  for  its  action,  and  the 
objects  carefully  kept  in  view  by  those  who  design,  construct,  and 
employ  it  as  one  of  the  most  useful  servants  of  mankind.  I  do 
not  think  this  has  been  done  before  with  anything  like  the  same 
simplicity  of  intention. 

There  are  very  wide  differences  in  externals,  but  in  essentials 
all  locomotives  without  exception,  are  the  same.  They  are 
survivals  of  the  fittest.  The  conditions  of  working  are  compara- 
tively inflexible  ;  and  the  more  closely  any  type  of  locomotive 
conforms  to  these  conditions  the  greater  are  the  chances  of  its 
success.  Yet  the  influence  of  nationality  and  climate  have 
made  themselves  felt ;  and  various  designs  may  be  regarded  as 
indigenous  to  particular  countries.  The  British  locomotive  is, 
above  all  others,  simple,  strong,  and  carefully  finished.  It  is 
intended  to  last  as  long  as  possible.  The  American  locomotive 
is  the  incarnate  spirit  of  opportunism.  It  is  intended  to  meet 
the  wants  of  the  moment ;  a  long  life  for  it  is  neither  desired  nor 
sought.  It  is  held  that  before  an  engine  can  wear  out  it  will  be 
superseded  by  something  bigger,  and  more  suitable  to  new  re- 
quirements and  conditions.  In  Europe  complication  is  favoured 
rather  than  disliked.  The  workmanship  is  as  a  rule  admirable ; 
but  simplicity  is  the  last  thing  studied.  In  all  cases  the  national 
character  appears  to  stamp  itself  on  machinery  of  every  kind. 

I  have  treated  the  modern  locomotive  from  three  points  of 
view,  namely,  as  a  vehicle,  as  a  steam  generator,  and  as  a  steam 
engine.  A  certain  amount  of  overlapping  is  unavoidable,  but  it 
will  not  confuse  the  issues. 


1NTBODUCTION  xi 

I  am  deeply  indebted  to  old  friends  and  acquaintances  for 
valuable  assistance.  I  have  only  had  to  ask  for  drawings  and 
information  to  obtain  them.  Among  others,  I  must  mention 
Mr.  J.  A.  Aspinall,  General  Manager,  Lancashire  and  Yorkshire 
Railway  ;  Mr.  G.  Churchward,  Great  Western ;  Mr.  Dugald 
Drummoud,  London  and  South  Western ;  Mr.  J.  Holden,  Great 
Eastern  ;  Mr.  G.  Hughes,  Lancashire  and  Yorkshire  ;  Mr.  Ivatt, 
Great  Northern;  Mr.  Wainwright,  S.  E.  and  C.  Railway; 
Mr.  G.  Whale,  London  and  North  Western  ;  and  Mr.  Theodore 
N.  Ely,  Chief  of  Motor  Power,  Pennsylvania  Railroad. 

I  have  not  attempted  to  quote  all  the  books,  British  and  foreign, 
and  papers  read  before  such  bodies  as  the  Institution  of  Civil 
Engineers,  or  Institution  of  Mechanical  Engineers,  which  have 
helped  me  ;  but  I  have  given  at  the  end  of  this  volume  a  short  list 
of  the  names  of  works  which  can  be  studied  with  advantage  by 
those  who  wish  to  know  more  about  the  locomotive  engine. 

Finally,  I  may  say  that  in  writing  I  have  carefully  kept  in 
view  the  needs  of  the  student.  I  have  endeavoured  to  make  the 
study  of  the  locomotive  attractive.  Unfortunately,  it  lends 
itself  in  many  ways  to  mathematical  treatment ;  and,  the 
mathematics  of  the  locomotive  are  very  far  from  being  a  good 
introduction  to  its  study.  It  may  be  added  that  in  practice  they 
play  but  a  secondary  part ;  and  this  principally  because  they  do 
not  always  fit  in  with  existing  conditions.  Anyone  who  has  the 
chance  of  standing  on  the  running  board  of  an  express  engine 
moving  at  fifty  or  sixty  miles  an  hour,  and  watching  the 
behaviour  of  the  valve  gear,  will  understand  just  what  I  mean. 

I  have  endeavoured,  as  I  have  said,  to  tell  my  readers  what 
the  modern  locomotive  is  and  why  it  is  what  it  is.  For  this 
purpose,  I  have  only  required  a  comparatively  small  number  of 
diagrams,  and  I  have  not  illustrated  any  types  of  locomotive. 
Photographs  will  be  found  of  these  by  the  hundred  in  other 
volumes,  where  they  serve  a  good  purpose  no  doubt.  They 
would  be  superfluities  in  this  book. 

VAUGHAN    PENDRED. 
STREA.THAM, 

1908. 


THE 

KAILWAY  LOCOMOTIVE 


SECTION    I 

THE  LOCOMOTIVE  ENGINE  AS  A  VEHICLE  » 
CHAPTEK   I 

FRAMES 

No  characteristic  of  the  locomotive  possesses  so  much  import- 
ance for  the  travelling  public  as  its  performance  as  a  vehicle. 
By  far  the  larger  proportion  of  the  serious,  or  even  terrible, 
accidents  which  occur  in  the  present  day  on  railways  in  this 
country  are  derailments.2  The  train  runs  off  the  track,  and  is 
more  or  less  smashed  up  according  as  the  speed  is  high  or 
moderate.  It  is  certain  that  in  nearly  all  cases  it  is  the  loco- 
motive that  first  leaves  the  line;  carriages  are  occasionally  derailed, 

1  The  locomotive  was  first  dealt  with  as  a  vehicle  by  the  late  D.  K.  Clark, 
in  "  Eailway  Machinery,"  published  in  1855. 

2  Among  the  more  recent  may  be  mentioned  the  derailment  of  a  Great 
Western  express  near  Loughor,  South  Wales,  on  October  3rd,  1904,  5  killed 
and  about  50  injured  ;  on  December  23rd  in  the  same  year  a  Great  Central 
train  was  derailed  at  Aylesbury,  4   killed  and  4  injured;    January  19th, 
1905,   Midland  train   derailed  near   Cudworth,   8   killed  and   20  injured  ; 
September   1st,    1905,    train  derailed   at  Witham  Junction   on   the   Great 
Eastern,    11  killed  and   40  injured;    July   1st,    1906,  American  boat  train 
wrecked  at  Salisbury,    South  Western  Railway  engine  upset  on  a  curve, 
28   killed  and   12   injured;    and   October  loth,  1907,    London  and   North 
Western  train  derailed  on  a  curve  at  Shrewsbury,  18  killed  and  many  injured. 

R.L:  B 


2  THE  KAILWAY  LOCOMOTIVE 

but  the  fact  that  each  is  tied  by  the  draw-bar  to  the  coach  next  in 
front  and  next  behind  it  tends  powerfully  to  prevent  the  escape 
of  the  wheels  from  the  rails.  Indeed,  there  are  well-known 
instances  in  which  a  pair  or  more  of  wheels  have  left  the  track, 
run  for  a  while  on  the  sleepers,  and  then  been  pulled  back  to  the 
rails  and  continued  running  very  little  the  worse.  No  one  has 
ever  heard  of  an  engine  getting  off  the  road  and  on  again 
automatically.  Furthermore,  if  an  engine  runs  badly,  it  may 
break  rails  and  injure  the  road  in  various  ways,  as  will  be 
explained  further  on.  A  bad  road  is  an  unsafe  road,  and  so, 
although  the  engine's  defects  may  not  be  those  which  induce 
derailments  directly,  they  may  be  exceedingly  mischievous  in 
other  respects. 

The  locomotive  is  subjected  to  two  classes  of  disturbance, 
the  one  external  to  it,  the  other  internal.  The  object  of  the 
designer  is  to  combat  or  get  rid  of  both,  and  as  w7e  proceed  it 
will  become  evident  that  the  task  is  by  no  means  easy  to 
perform. 

It  must  be  steadily  kept  in  mind  that  the  locomotive  and  the 
permanent  way  are  but  two  parts  of  the  same  machine.  The 
rails  bear  precisely  the  same  relation  to  the  engine  that  the  V 
grooves  of  a  planing  machine  do  to  the  sliding  table.  Good 
planing  cannot  be  done  unless  the  grooves  and  slides  are  in  order ; 
and  smooth,  safe  travelling  is  impossible  unless  the  engine  and 
the  road  are  both  in  excellent  condition,  and  in  as  nearly  as  may 
be  perfect  mechanical  adjustment.  If  the  road  is  bad,  uneven, 
and  weak,  the  disturbing  effects  may  be  so  great  as  to  mask 
defects  in  the  engine.  On  the  other  hand,  the  road  may  be  so 
excellent  that  the  inherent  defects  of  the  engine  may  be  forced 
into  prominence,  the  internal  factors  of  disturbance  then  masking 
such  defects  in  the  track  as  may  still  exist. 

Let  us  deal  with  the  external  disturbing  forces  first. 

If  the  track  was  dead  straight  and  absolutely  smooth,  level 
and  rigid  ;  if  the  wheels  were  quite  cylindrical  and  carefully 
balanced,  then  a  vehicle  might  be  run  at  any  speed  without  the 
least  danger.  No  force  would  solicit  it  to  jump  off  the  rails  or 
overturn.  These  conditions  represent  the  maximum  limit  of 


FEAMES  3 

safety.  Just  in  so  much  as  these  conditions  remain  unfulfilled 
will  the  probability  of  derailment  or  upsetting  be  augmented. 
In  practice  the  maximum  limit  can  never  be  attained.  The  rails 
are  never  wholly  smooth,  level,  and  unyielding,  and  any  vehicle 
intended  to  run  on  them  with  safety  must  be  provided  with 
expedients  by  which  the  effect  of  the  imperfections  in  the  track 
on  the  stability  of  the  machine  will  be  minimised.  The 
influence  of  imperfections  may  be  divided  into  two  sections,  one 
vertical,  the  other  horizontal.  Thus  the  rails  not  being  dead 
level,  the  wheels  have  to  run  up  and  down  so  many  steel  waves 
more  or  less  long  and  seldom  coincident  on  both  rails.  To  reduce 
the  jumping  motion  springs  are  placed  between  the  axle  boxes 
and  the  body  of  the  vehicle.  To  neutralise  the  effect  of  horizontal 
imperfections  a  certain  amount  of  lateral  flexibility  is  imparted 
to  the  vehicle.  Curves  may  be  regarded  as  horizontal  defects  in 
the  permanent  way ;  and  to  help  the  locomotive  to  deal  with  the 
centrifugal  effort  the  outer  rail  is  raised  above  the  level  of  the 
inside  rail  by  an  amount  fixed  by  the  radius  of  the  curve  and  the 
speed  at  which  it  is  traversed.  These  are  general  principles  ; 
we  may  now  proceed  to  consider  them  in  more  detail. 

Every  locomotive  consists  of  a  framework  or  chassis  supported 
by  springs  on  wheels.  The  framework  carries  in  its  turn  a 
boiler,  and  an  engine  with  two,  three,  or  four  horizontal  or 
nearly  horizontal  cylinders,  two  being  the  usual  number.  The 
framing  may  be  regarded  as  the  link  between  all  the  various 
parts  of  the  whole  locomotive.  There  are  two  types  of  framing, 
namely,  the  plate  frame  and  the  bar  frame.  The  latter  is  very 
little  used  in  this  country ;  the  former  very  little  used  in  the 
United  States.  In  certain  cases  it  is  not  easy  to  say  to  which 
type  the  framing  belongs ;  but  these  are  very  exceptional. 

The  plate  frame  is  a  rectangular  steel  structure,  composed 
mainly  of  two  plates  extending  from  the  leading  to  the  trailing 
end  of  the  engine.  Their  depth  and  thickness  vary  in  different 
designs  ;  but  it  may  be  taken  generally^that  the  plates  are  1  inch 
to  H  inch  thick,  and  18  inches  to  2  feet  deep.  They  are  secured 
to  each  other  by  cross  plates  and  angle  steels.  These  main 
frames  are  usually  supplemented  by  secondary  frame  plates  much 

B2 


4  THE  EAILWAY   LOCOMOTIVE 

lighter  and  narrower,  on  top  of  which  rests  a  flat  steel  plate, 
known  as  the  "  running  board,"  along  which  the  driver  can  walk, 
and  so  oil  and  inspect  his  engine  while  it  is  running.  Little  or 
nothing  of  the  main  frame  can  be  seen  in  many  engines,  because 
it  is  concealed  by  the  wheels,  splashers,  running  board,  &c. 

It  is  of  the  utmost  importance  to  the  good  and  safe  running  of 
the  engine  that  the  framework  shall  always  remain  quite  rigid; 
that  the  angles  between  the  longitudinal  and  the  cross  plates 
shall  be  true  right  angles ;  and  that,  in  a  word,  no  twisting  in 
any  plane  shall  take  place.  If  the  track  were  a  dead  level  there 
would  be  no  risk  of  twisting;  but  it  is  not  level,  and  one  corner 
of  the  engine  may  be  raised  by  a  wheel  on  a  ridge,  while  another 
is  lowered  because  the  nearest  wheel  is  in  a  hollow.  Changes  in 
the  amount  and  direction  of  the  stress  occur  every  moment.  The 
stresses  are  far  too  complicated  to  permit  of  mathematical  treat- 
ment. The  designer  never  attempts  to  calculate  their  amounts. 
He  adapts  the  proportions,  and  method  of  riveting  or  bolting, 
which  have  been  found  by  experience  to  be  the  best.  Any  con- 
siderable change  in  design  involves  something  of  an  experiment. 
Eisks  are  got  over,  however,  by  the  simple  expedient  of  making 
things  very  strong. 

Frames  maybe  either  "inside"  or  "outside."  In  the  first 
case  the  journals  of  the  axles  are  inside  the  wheels.  In  the  latter 
case  they  are  outside  the  wheels.  The  distance  between  the 
bosses  or  hubs  of  the  wheels  cannot  for  a  line  of  4  feet  8J  inches 
gauge  be  more  than  4  feet  5J  inches,  and  with  inside  cranks 
this  reduces  the  length  of  the  bearing  or  journal  within  narrow 
limits.  If  the  journals  are  placed  outside,  then  the  bearing  can, 
of  course,  be  made  as  long  within  reasonable  limits  as  may  be 
desired ;  the  load  per  square  inch  is  reduced,  and  a  substantial 
advantage  gained.  But  the  cross  breaking  stress  on  the  crank 
axle  is  augmented ;  and  besides,  with  coupled  engines,  cranks 
fitted  on  the  ends  of  the  axles  become  necessary,  and  the  design 
of  the  engine  ceases  to  be  compact.  With  inside  frames  no 
crank  arms  are  used,  the  pins  being  secured  in  radial  prolonga- 
tions of  the  wheel  bosses. 

So   long   as   engines   remained  small,  and  particularly  with 


FRAMES  5 

single  engines,  either  the  outside  bearing  or  a  combination  of 
the  outside  and  inside  bearings  remained  in  favour.  The  com- 
bination was  in  a  way  a  compromise.  Two  short  journals  were 
used,  one  inside,  the  other  outside  the  wheel,  which  was  then  so 
far  supported  that  even  if  the  axle  broke  anywhere  but  in  a 
journal  the  wheel  could  still  carry  its  load,  and  the  engine  would 
not  be  derailed.  The  advent  of  the  big  coupled  engine,  however, 


FIG.  1. — Stephenson  inside  axle  box. 

gave  the  coup  de  grace  to  outside  bearings,  and  they  are  very 
seldom  seen  now  except  on  old  locomotives.  But  from  the  first 
there  was  trouble.  The  crank  axles  of  those  days  were  not  very 
trustworthy  forgings,  and  as  far  back  as  1838  we  find  Eobert 
Stephenson  putting  in  no  fewer  than  four  inside  frames,  which 
were  thus  described  by  Mr.  W.  N.  Marshall  many  years  ago. 
This  description  and  the  illustrations,  Fig.  1,  are  worth  pro- 
ducing, because  the  inside  frame  to  sustain  the  crank  shaft 
against  the  thrust  and  pull  of  the  connecting-rod  is  still  used. 
The  axle  box  also  shows  the  system  of  wedges  for  tightening  the 


6  THE  KAILWAY  LOCOMOTIVE 

bearings  on  the  shaft,  and  also  in  the  horn-plates.  All  driving 
axle  boxes  are  fitted  with  wedges  to  take  up  wear  between  the 
axle  boxes  and  the  faces  of  the  horn-plates,  but  only  a  single 
wedge  is  used,  as  the  small  longitudinal  displacement  cannot 
affect  the  running  of  the  engine. 

"  Four  wrought  iron  frames  A  A,  3J  inches  deep  and  f  inch 
thick,  are  fixed  between  the  smoke-box  and  the  fire-box  to 
afford  additional  strength  to  the  engine  by  securing  firmly  the 
back  plate  of  the  smoke-box  in  which  the  cylinders  are  fixed,  and 
which  has  to  bear  the  whole  strain  of  the  working  of  the  engine. 
These  inside  frames  have  also  bearings  in  them  for  the  cranked 
axle,  and  hold  it  steadily  against  the  action  of  the  connecting 
rods,  by  which  it  is  strained  alternately  in  opposite  directions. 
They  are  attached  to  the  smoke-box  by  means  of  T-shaped  pieces 
of  iron,  which  are  riveted  on  to  the  inner  and  side  plates,  and 
are  bolted  to  the  ends  of  the  frame.  The  two  middle  frames  are 
made  to  approach  each  other,  and  are  welded  together  at  the 
back  end,  so  that  there  are  only  three  bearings  on  the  cranked 
axle.  The  inside  bearings  shown  in  Fig.  1  are  formed  by 
thickening  the  frame  plate  A  to  2^  inches  at  B.  It  is  made  into 
two  inclined  limbs  C  C,  and  between  which  are  placed  the  two 
bearings  G  G,  by  which  the  axle  is  embraced.  These  are  tightened 
and  adjusted  by  means  of  wedges  E  E,  taken  up  by  screws  and 
nuts  F  F.  The  lower  ends  of  C  C  are  united  by  a  tube  D  placed 
between  them,  and  a  bolt  and  nut  passed  through  it." 

The  plate  frame  possesses  a  good  deal  of  lateral  elasticity 
through  a  small  range,  and  this  is  of  use.  In  the  early  days  of 
locomotive  engines,  Messrs.  Sharp,  Eoberts  &  Co.,  Atlas  Works, 
Manchester,  built  hundreds  of  engines  the  side  frames  of  which 
were  ash  planks  about  3  inches  thick,  secured  between  two  iron 
flitch  plates.  For  the  comparatively  small  locomotives  of  the 
period  these  frames  were  most  excellent.  Fig.  2  is  an  elevation 
of  a  standard  type  of  engine  constructed  by  Kobert  Stephenson 
&  Co.  It  was  closely  followed  in  design  by  Sharp,  Koberts  &  Co. 
The  illustration  is  given  here  because  the  general  features 
of  the  design  were  copied  for  .many  years,  and  the  arrange- 
ment of  the  springs  is  used  to  this  day.  A  few  engines  are 


EEAMES  7 

still  running  with  them  ;  indeed,  at  one  period  the  ash  side 
frame  was  in  extensive  use.  In  the  present  day,  however,  only 
the  plate  and  the  bar  frame  are  used.  This  last  was  introduced 
by  Mr.  Bury,  of  the  firm  of  Bury,  Curtis  &  Kennedy,  about 
the  year  1833.  As  its  name  denotes,  it  is  built  up  of  a  number 
of  rectangular  bars,  either  welded  together  or  secured  to  each 
other  with  rivets,  dovetails,  and,  in  most  cases,  bolts.  These 


FIG.  2. — Stephenson  standard  locomotive,  1838. 

last  are  turned  dead  true,  and  are  made  tight  driving  fits  for  the 
holes  into  which  they  are  put.  In  the  early  days  the  United 
States  possessed  no  rolling-mills  which  could  make  plates  fit  for 
side  frames.  The  average  smith  possessed  skill  enough  to  build 
up  frames  from  bars  forged  under  a  water-driven  tilt  hammer. 
So  the  bar  frame  found  favour,  and  although  the  United  States 
can  supply  steel  plates  of  any  required  dimensions  now,  the  bar 
frame  is  still  retained.  It  is  a  very  good  frame,  and  possesses 
some  advantages  over  the  plate  frame,  but  it  is  expensive  to 


8  THE  RAILWAY  LOCOMOTIVE 

make  and  very  costly  to  repair.  The  plate  frame  is  so  simple 
that  its  essentials  and  its  qualifications  for  the  work  it  has  to  do 
can  be  understood  in  a  moment.  This  is  far  from  being  the  case 
with  the  bar  frame,  and  an  account  of  some  of  the  modifications 
which  it  has  undergone  is  introduced  here  because  its  history 
sets  forth  almost  directly  the  nature  of  the  stresses  to  which  the 
framing  of  a  locomotive,  no  matter  how  constructed,  is  exposed, 
and  the  way  in  which  development  proceeds.  For  the  drawings 
the  author  is  indebted  to  the  pages  of  the  Railroad  Gazette.  In  the 
United  States  the  bar  frame  has  always  been  made  in  two  pieces 
as  shown  in  Fig.  3,  the  front  end  carrying  the  cylinders  and  the 
back  piece  the  horn  blocks  for  the  axle  bearings.  Bury  almost 
invariably  forged  his  frames  in  one  piece,  which  he  could  easily 
do  because  the  engines  were  small,  and  it  must  not  be  forgotten 
that  when  the  plate  frame  first  came  into  being  it  was  made  of 
iron  in  three  lengths  with  two  welds.  The  modern  frame  is  a 
continuous  plate  of  steel.  The  great  trouble  has  always  been  with 
the  joints.  In  Fig.  3,  which  explains  this,  is  shown  the  arrange- 
ment used  in  the  earlier  days — say  1845.  The  key  was  supposed 
to  save  the  vertical  bolts  some  shear.  While  the  cylinders  were 
small  this  plan  answered  fairly  well ;  with  larger  cylinders  the 
bolts  stretched  and  the  nuts  worked  loose.  Then  came  Fig.  4, 
with  the  principal  'bolts  a  hard  driving  fit,  and  in  double  shear. 
Double  keys  were  used,  but  they  twisted,  and  did  not  then  help 
the  bolts.  This  was  followed  by  Fig.  5.  Still  the  longitudinal 
alternating  stresses  were  too  much  for  the  joint.  Then  came 
Figs.  6  and  7,  all  still  depending  on  bolts. 

In  some  designs  the  frames  had  double  bars — they  are  called 
"  rails  "  in  the  States — as  seen  in  Figs.  8,  9,  10,  11,  and  12.  In 
these  it  is  clear  that  bolting  had  been  carried  as  far  as  possible, 
and  for  the  more  modern  big  engines  a  somewhat  different 
method  of  construction  has  been  adopted,  as  shown  in  Figs.  13 
and  14.  Here  the  two  front  bars  or  "rails"  have  been  united 
in  a  single  deep  slab,  to  which  the  cylinders  are  bolted.  The 
first  frames  made  in  this  way  had  the  fastening  to  the  main 
frame  made  as  in  Fig.  13,  but  they  have  to  some  extent  been 
superseded  by  the  plan  shown  in  Fig.  14. 


Fig. 16. 
FIGS.  3 — 16. — The  development  of  the  bar  frame. 


10  THE  EAILWAY  LOCOMOTIVE 

Seeing  how  unsatisfactory  in  certain  respects  the  built-up  bar 
frame  has  been,  at  least  for  large  locomotives,  it  is  not  surprising 
that  attempts  have  been  made  to  do  away  with  it.  The  United 
States  locomotive  designer  is  obstinately  determined  not  to  have 
the  plate  frame,  and  he  has  turned  his  attention  to  the  produc- 
tion of  cast  steel  frames  in  whole  or  in  part.  One  is  illustrated 
in  Fig.  15.  The  back  ends  of  the  frame  being  spared  the  worst 
of  the  longitudinal  stresses  are  very  much  what  they  always 
were.  One  is  illustrated  in  Fig.  16.  It  must  be  understood  that 
the  engravings  given  here  do  not  represent  every  kind  of  bar 
frame  in  use.  It  lends  itself  to  wide  diversities  of  treatment,  and 
is  much  favoured  on  several  European  railways. 

The  plate  frames  are  secured  to  each  other  by  cross  plates, 
usually  four  in  number — that  is  to  say,  one  at  the  trailing  end, 
another  just  in  front  of  the  fire-box,  the  leading  head  stock 
carrying  the  front  buffer  beam,  and  a  very  heavy,  strong  frame- 
work supporting  the  bogie.  There  is  besides  the  ''spectacle 
plate"  or  "  motion  plate,"  which  is  a  steel  casting  supporting 
the  outer  ends  of  the  piston-rod  guides,  and  the  valve  motion. 
The  cylinders  are  in  the  present  day  usually  cast  in  one  piece, 
and  being  bolted  between  the  frames,  stiffen  them  still  further. 
As  has  been  said,  the  stresses  to  which  the  framing  is  exposed 
are  very  great.  Thus,  in  large  engines,  that  due  to  the  steam 
effect  on  the  pistons  may  reach  as  much  as  fifty  tons.  Then 
there  is  not  only  the  weight  of  the  boiler  and  the  water  in  it,  but 
the  various  stresses  set  up  by  the  arrested  momentum  of  the 
boiler  when  the  engine  lurches  or  rolls. 

For  the  bar  frame  it  is  claimed  that  it  is  on  the  whole  lighter 
than  the  plate  frame,  and  that  various  parts  may  be  more 
conveniently  secured  to  it,  while  it  gives  unexampled  facilities 
for  access  to  the  mechanism.  But  it  has  been  found  essential 
to  stiffen  it  by  plates  bolted  to  the  frame  and  to  the  boiler,  a 
practice  which  has  been  almost  given  up  in  this  country,  as 
grooving  is  very  likely  to  take  place  where  the  stiffening  plate  is 
riveted  to  the  boiler  shell.  This  grooving  is  the  result  of  minute 
bendings  backward  and  forward  of  the  boiler  plate  just  where  the 
frame  plate  is  riveted  to  it. 


FRAMES 


11 


The  frame  has  to  be  fitted  with  wheels  and  springs.  The 
axles  revolve  in  boxes,  either  made  entirely  of  gun  metal  or  of 
pressed  steel  lined  with  brass  or  gun  metal.  The  practice  of 
making  axle  boxes  of  cast  iron  has  long  since  been  given  up. 
At  one  time  they  were  forged  under  a  steam  hammer ;  but  about 
1872  the  late  Mr.  John  Haswell,  locomotive  superintendent  of 
the  Austrian  State  Kailways,  invented  and  constructed  a  very 
powerful  hydraulic  forging  press  in  which  axle  boxes,  cross  heads, 
and  such  like  were  pressed  out  of  white  hot  steel  billets,  at  the 
rate  of  about  half  a  minute  for  each.  An  axle  box  is  shown 
diagrammatical ly  in  Fig.  17. 

To  the  plate  frames  are  bolted  steel  castings  or  forgings 
called  horn  plates,  in  which 
the  axle  boxes  can  move  up 
and  down  through  a  range 
in  Great  Britain  usually  of 
about  2  inches,  in  France, 
often  of  nearly  twice  as  much, 
the  springs  being  longer  and 
more  flexible  than  in  Great 
Britain.  When  plate  springs 
are  used,  they  either  rest 
directly  or  through  the  medium  of  struts  on  the  tops  of  the  axle 
boxes  as  shown  in  Fig.  2.  In  some  cases,  however,  the  springs 
are  placed  under  the  axle  boxes  and  secured  to  them  by  links,  as 
in  Fig.  17.  Here  A  is  the  axle,  B  brass,  C  axle  box,  F  the. 
spring,  the  ends  of  which  are  supposed  to  rest  on  rubbing  plates 
under  the  frame.  The  spring  is  coupled  to  the  axle  box  by  the 
links  E  and  the  pin  D.  An  example  of  the  overhead  spring  is 
given  in  Fig.  2.  Coiled  springs  are  favoured,  because  they  save 
space.  They  are  invariably  worked  in  compression. 

In  the  United  States  almost  always,  in  this  country  frequently, 
the  ends  of  springs  are  coupled  to  each  other  by  what  are  known 
as  balance  beams  or  compensating  levers.  An  example  is  shown 
in  Fig.  18,  which  illustrates  a  portion  of  an  American  bar 
frame  locomotive.  A  is  a  compensating  lever;  at  C  is  seen 
the  end  of  another  lever.  In  this  way  stresses  are  eased,  and 


FIG.  17.— Axle-box. 


12  THE  EAILWAY  LOCOMOTIVE 

the  engine  runs  more  smoothly.  For  let  it  be  supposed  that 
each  spring  works  by  itself,  and  has  no  connection  with  its 
fellow;  then  it  is  easily  understood  that  when  a  wheel  is  passing 
over  the  summit  of  a  wave  in  the  rail,  a  large  part  of  the  load 
will  be  taken  off  a  neighbouring  wheel  in  a  hollow,  and  a  corre- 
sponding stress  will  be  thrown  on  the  whole  frame,  &c.  If, 
however,  the  ends  of  the  springs  are  coupled  by  a  balance  beam, 
then  a  portion  of  the  extra  load  on  the  first  spring  will  be  trans- 
ferred to  the  second,  and  the  engine  will  run  with  more  flexibility. 
The  risk  of  breaking  springs  or  axle  boxes  is  besides  much 


PIG.  18. — Compensating  lever. 

.reduced.  Many  engineers  in  this  country  hold,  however,  that  on 
a  first-class  road  balance  beams  are  quite  unnecessary ;  and,  by 
imparting  too  much  resilience  to  the  engine  as  a  vehicle,  tend  to 
promote  rolling  and  pitching,  and  even  to  make  it  unsafe  at  high 
speeds.  When,  however,  an  engine  encounters  a  steep  incline 
which  does  not  "melt  into  the  level"  as  it  ought  to  do,  the 
leading  springs  may  have  so  much  extra  load  thrown  on  them 
that  they  will  break.  Again,  in  running  off  the  incline  on  to  the 
level  again  an  extra  load  may  be  thrown  on  the  driving  wheel 
springs.  The  evil  has  in  some  cases  been  so  pronounced  that 
the  road  has  been  improved  by  modulating  the  incline  at  the 
instance  of  the  locomotive  superintendent. 


FBAMES  13 

So  far  only  vertical  stresses  have  been  considered,  and  the 
vehicle  has  been  supposed  to  traverse  only  a  dead  straight  road. 
We  have  now  to  regard  it  from  another  aspect.  Eailways  abound 
in  curves,  and  these  have  to  be  traversed  at  various  speeds, 
sometimes  very  high. 

The  smallest  locomotives,  such  as  are  used  by  contractors  on 
civil  engineering  works,  alone  have  four  wheels  and  no  more. 
Until  a  comparatively  recent  period  all  but  exceptional  engines 
were  carried  on  six  wheels.  The  practice  then  arose  of  carrying 
the  leading  ends  on  a  four-wheeled  bogie,  and  this  gave  eight 
wheels.  A  further  increase  in  length  brought  in  a  fifth  pair 
under  the  footplate.  An  addition  in  size  gave  six  coupled 
driving  wheels  instead  of  four.  The  practice  has  recently  grown 
up  of  indicating  the  number  of  wheels  thus :  2 — 4 — 2,  which 
means  2  leading,  4  driving,  and  2  trailing  wheels.  Again, 
4 — 2 — 2  means  a  4-wheeled  bogie,  2  driving  wheels  and  2 
trailing  wheels,  and  so  on.  In  goods  engines  as  many  as  twelve 
coupled  wheels  are  used,  for  the  most  part  in  the  United  States, 
where  at  certain  seasons  of  the  year  trains  carrying  as  much  as 
2,500  to  3,000  tons  of  grain  are  hauled  at  speeds  of  ten  or  twelve 
miles  an  hour  from  eastern  corn  lands  to  western  seaports. 

The  so-called  wheel  base  of  a  locomotive  is  the  distance  from 
the  centre  of  the  leading  to  the  centre  of  the  trailing  axle ;  the 
wheels  are  all  firmly  secured  on  the  axles  by  forcing  them  on  by 
hydraulic  pressure,  so  that  they  must  turn  together.  The  end- 
wise play  of  the  axles  in  their  bearings,  and  of  the  boxes  in  the 
horn  plates,  is  but  a  fraction  of  an  inch.  When  the  engine 
stands  on  a  curve,  in  order  that  all  the  wheels  may  fit  it  the  frame 
ought  to  bend  to  the  same  radius  as  the  curve.  This  is  im- 
possible, yet  it  would  also  be  a  mechanical  impossibility  for  a 
rigid  vehicle  with  six  wheels  to  get  round  a  rigid  curve  if  the 
flanges  of  the  wheels  fitted  the  rails  closely.  The  difficulty  is 
overcome  in  various  ways.  In  the  first  place  the  rails  are  always 
about  half  an  inch  wider  apart  than  the  distance  between  the 
flanges.  This  distance  is  increased  to  about  an  inch  on  sharp 
curves.  Secondly,  one  or  more  pairs  of  wheels  about  the  mid- 
length  of  the  engine  are  sometimes  made  "  blind,"  that  is  to  say, 


14  THE  EAILWAY  LOCOMOTIVE 

they  are  without  flanges.  Thirdly,  one  or  more  of  the  axles  are 
provided  with  boxes  which  can  slide  right  or  left  in  the  horn 
plates,  a  couple  of  inches  each  way.  They  are  kept  normally 
central  by  strong  coiled  springs ;  and  lastly,  there  is  the  bogie. 

Any  reader  interested  is  advised  to  set  out  a  curve  on  a 
drawing-board  and  set  out  a  vehicle  on  it.  He  will  see  that  no 
matter  how  many  wheels  the  vehicle  has,  it  will  do  its  best  to 
arrange  itself  as  a  chord  to  the  arc.  Now  a  four-wheeled  vehicle 
can  always  do  this  without  trouble,  and  the  axles  will  approxi- 
mate in  position  to  radii  of  the  curve.  In  this  country  it  may 
be  taken  that  the  minimum  radius  of  curves  traversed  at  any 
but  the  very  slowest  speed  is  about  6  chains,  or  say  400  feet. 
Let  our  four-wheeled  vehicle  be  a  bogie  with  a  wheel  base  of 
6  feet;  it  will  be  seen  that  to  all  intents  and  purposes  both 
axles  are  radii  to  the  curve,  with  an  approximation  to  the  truth 
so  close  that  the  difference  must  be  measured  by  small  fractions 
of  an  inch.  Such  a  curve,  therefore,  could  be  traversed  by  the 
bogie  almost  as  easily  as  if  the  track  were  straight.  If  now  we 
take  an  engine  with  four  wheels  coupled  near  one  end,  and 
support  the  other  end  on  a  bogie,  all  the  axles  will  virtually 
radiate  to  the  centre  of  the  curve.  But  a  horizontal  centre  line 
drawn  through  either  a  pair  of  coupled  wheels  or  a  pair  of  bogie 
wheels  will  be  a  tangent  to  the  curve,  as  the  engine  frames 
extend  for  several  feet  in  advance  of  the  leading  pair  of  driving 
wheels,  and,  being  a  tangent  to  the  curve,  it  follows  that  a  central 
line  prolonged  along  this  tangent  cannot  fall  on  the  centre  of  the 
bogie,  but  at  some  place  outside  it.  Thus  to  get  the  best  results 
the  whole  bogie  must  be  able  to  move  inwards,  or,  what  comes 
to  the  same  thing,  the  engine  frame  must  be  permitted  to  retain 
its  tangential  position  while  rounding  the  curve. 


CHAPTER    II 

BOGIES 


AT  first  sight  the  bogie  appears  to  be  a  very  simple  thing  whose 
action  can  readily  be  understood.  In  point  of  fact,  however, 
this  is  not  the  case,  and  the  bogie  plays  so  important  a  part  in 
the  present  day  that  both  the  theory  of  it  and  practice  with  it 


FIG.  19. — Bissell  bogie. 

deserve  very  careful  consideration.  It  originated  in  the  United 
States.  It  is  claimed  for  it  that  it  was  an  English  invention, 
because  small  four-wheeled  coal  mine  trucks  were  called  "bogies." 
But  in  the  United  States  what  we  term  "  bogies"  always  were 
and  are  still  called  "  trucks."  The  first  railways  made  in 
America  were  very  bad  indeed,  much  worse  than  English  rail- 
ways, and  the  four-wheeled  locomotives  were  continually  running 
off  the  road,  particularly  on  curves.  It  was  decided  then  to  copy 


16 


THE  EAILWAY  LOCOMOTIVE 


the  ordinary  horse-drawn 
vehicle  and  fit  locomotives 
with  a  species  of  fore 
carriage.  For  convenience 
this  was  made  at  first  with 
four  wheels,  while  the 
engine  proper  had  but  two. 
No  traversing  gear  was 
required,  because  the  lead- 
ing end  of  the  engine  could 
follow  the  bogie  round  the 
curve.  After  a  time  it  was 
found  that  coupled  wheels 
were  necessary.  Traversing 
then  became  essential,  and 
Mr.  Bissell,  an  American 
engineer,  invented  the 
"  Bissell  truck,"  which  had 
two  wheels  while  the  loco- 
motive had  four.  His  was 
a  very  clever  device  much 
used  at  one  time  in  the 
United  States,  and  still 
enjoying  favour  there.  The 
accompanying  diagram,  Fig. 
19,  will  tell  the  reader 
almost  at  a  glance  what  it 
is.  It  is  a  plan  of  an  im- 
proved "  pony  "  used  on  the 
Great  Northern  Eaiiway. 
As  first  used  the  pony  had, 
as  stated  above,  but  one 
pair  of  wheels.  Afterwards 
four  wheels  were  employed 
and  it  ceased  to  be  a  pony. 
In  this  country  it  was  fitted 
to  all  the  locomotives 


BOGIES  17 

designed  by  the  late  Sir  John  Fowler  for  the  Metropolitan 
Kailway.  We  have  only  to  substitute  a  bogie  with  four 
wheels  for  the  single  pair  in  Fig.  19,  and  the  description  will 
apply.  A  frame  A  enclosed  the  axle;  to  the  back  end  of  the 
frame  was  bolted  a  heavy  flat  bar  triangle  or  tail  D ;  through 
the  eye  on  the  end  of  this  passed  a  bolt  C  ;  and  round  this 
bolt  as  a  pivot  the  truck  could  describe  an  arc,  swaying  to  the 
right  and  left.  It  was  essential,  however,  that  it  should  always 
tend  to  keep  in  the  centre  line  of  the  engine.  To  ensure  this, 
the  axle  casing  was  fitted  at  the  forward  end  with  flat  trans- 
verse plates  provided  with  inclined  planes.  The  cross  beam 
under  the  engine  was  fitted  with  similar  planes  B  which  rested 
on  those  first  named.1  Whenever  the  bogie  moved  to  the  right 
or  the  left  it  had  to  lift  the  leading  end  of  the  engine,  which, 
tending  to  slide  down  the  inclined  planes,  always  returned  the 
truck  to  its  normal  position  as  soon  as  the  locomotive,  having 
passed  over  the  curve,  entered  the  straight  again.  In  the  United 
States  a  somewhat  different  arrangement  is  in  use.  The  leading 
end  of  the  engine  is  hung  by  links  from  the  bogie,  which 
virtually  shorten,  as  the  engine  moves  to  left  or  right,  in  a  way 
quite  obvious.  The  modern  bogie  is  only  a  modification  of  the 
original.  Figs.  20  and  21  show  a  bogie  on  the  Great  Northern 
Kailway  fitted  with  swing  links. 

A  A  are  the  cylinders,  S  the  valve  chest.  The  cylinders,  and 
with  them  the  leading  end  of  the  engine,  rest  on  a  heavy  casting  D 
circular  in  plan  to  allow  the  bogie  to  turn  round  the  pin  P.  This 
iron  casting  rests  in  turn  on  one  of  steel  M.  This  casting  has 
no  power  of  traversing — it  may  be  regarded  as  part  and  parcel 
of  the  engine.  B  B  shows  one  of  two  cross  beams.  The 
entire  weight  of  the  leading  end  of  the  engine  is  supported 
by  four  links  L  L,  and  will  always  tend  to  return  to  the 
position  shown,  just  as  a  pendulum  seeks  its  lowest  position. 
Traversing  is  obtained  very  simply  in  this  way.  A  saucer-shaped 
steel  plate  is  pinned  on  the  bottom  of  the  upper  casting,  and  a 

1  In  the  Great  Northern  pony,  the  spring  pedestals  rest  directly  on  the  tops 
of  the  axle  boxes  E.  The  circles  show  the  enlarged  ends  of  the  pedestals 
made  of  brass  to  reduce  friction. 

R.L.  C 


18  THE   E  AIL  WAY  LOCOMOTIVE 

similar  plate  is  laid  under  it  in  M.  This  permits  the  bogie  to 
rock.  One  corner  may  rise  while  another  falls,  in  a  way  that 
will  be  explained  further  on. 

It  is  desirable  that  the  reader  should  clearly  understand  what 
a  complete  bogie  is  like,  which  it  is  not  easy  to  do  from  sectional 
drawings.  To  this  end  Figs.  23  and  24  are  given.  The  bogie 
frame  is  usually  a  built-up  structure  like  an  engine  frame.  If, 
however,  it  could  be  produced  with  a  less  number  of  riveted 
and  bolted  joints  a  substantial  advantage  would  be  gained.  The 
Leeds  Forge  Company,  Limited,  has  for  years  turned  out  great 

quantities  of  flanged  furnaces,  &c.,  the 
flanging  being  done  by  an  hydraulic 
press  in  a  way  which  will  be  understood 
from  the  annexed  diagram  (Fig.  22). 

I I  Here  A  is  the  plate  to  be  bent,  let 

' •>          - — '  us  suppose,  to  the  shape  of  the  lid  of 

a  pill  box.     C  is  the  hollow  top  of  a 
hydraulic  press  of  which  D  is  the  ram. 
B  is  a  fixed  circular  block,  just  as  much 
1    smaller  all  round  than  C  as  the  plate  is 

thick.     The  flat  circular  plate  is  heated 
FIG.  22. — .Flanging  press.       ,          -i    n       -i  i  111          i 

to  a  dull  red  heat  and  placed  as  shown. 

Then  the  ram  is  pumped  up,  and  the  plate  is  forced  into  C,  curling 
up  all  round  the  edges  without  crumpling  or  buckling.  Of  course 
a  trough  could  be  made  in  the  same  way  by  using  a  long  mould 
and  several  hydraulic  rams.  The  system  is  in  use  all  over  the 
world  ;  but  certain  firms  make  a  speciality  of  pressed  work.  The 
Leeds  Forge  Company  includes  bogies  of  all  kinds.  Figs.  23  and 
24  illustrate  two  standard  wagon  bogies  made  of  pressed  steel. 
Fig.  23  is  an  open-ended  bogie  ;  the  sides  are  united  by  the 
cross  beams  near  the  middle.  On  the  top  of  these  is  bolted  a 
casting  with  a  circular  boss.  A  similar  boss  is  bolted  under  the 
wagon  body,  which  rests  on  it,  a  pin  being  dropped  through 
both  round  which  the  bogie  swivels.  As  there  is  a  bogie  at  each 
end  of  the  wagon  no  traversing  motion  is  required.  On  each 
side  frame  are  seen  bearing  blocks  on  which  a  part  of  the  weight 
is  carried.  The  axle  boxes  and  the  coiled  springs  in  compression 


BOGIES 


19 


FIG.  23. — Open  end  bogie. 


FIG.  24. — Closed  end  bogie. 

which  transmit  the  load  to  them  and  the  horn  plates  are  all  very 
clearly  shown.  Fig.  24  is  a  wagon  bogie  with  closed  ends  and 
leaf  instead  of  coiled  springs.  It  is  not  fitted  with  brakes ;  the 
open-ended  bogie,  Fig.  23,  is.  The  hinged  hanger  gear  for  them 
can  be  seen  bolted  to  the  cross  beams.  An  enormous  number  of 

c2 


20 


THE  RAILWAY  LOCOMOTIVE 


pressed  steel  bogies  is  in  use;  the  Leeds  Forge  Company  alone  has 
made  15,000  of  them. 

Figs.  25,  26,  and  27  illustrate  a  standard  engine  bogie  designed 
by  Mr.  James  Holden,  locomotive  superintendent  of  the  Great 
Eastern  Railway.  Traverse  is  controlled,  not  by  metallic  springs, 


FIG.  25.— Standard  bogie,  Great  Eastern  Bail  way. 

but  by  indiarubber  discs,  which  Mr.  Holden  prefers  because 
they  deaden  the  shock  when  an  engine  takes  a  curve.  Engines 
fitted  in  this  way  ride  very  easily.  Sliding  takes  place  on  the 
surface  B.  There  is  a  cushion  of  indiarubber,  0,  between  A  and 
the  sliding  portion  above  the  top  of  the  surface  B.  The  amount 


BOGIES 


21 


-3  -\8  Centres  of  journals 


FIG.  26. — Standard  bogie,  Great  Eastern  Bailway. 


of  traverse  is  1 J  inches.    The  slide  is  controlled  by  the  six  india- 
rubber  pads  shown  in  the  sections.     The  casting  A  is  bolted 


FIG.  27. — Details  bogie,  Great  Eastern  Kail  way. 

to  the  main  frame,  A1   being  one  of  the  bolts  used  for  this 
purpose. 

On  the  Great  Western  Bailway  Mr.  Churchward  uses  a  bogie 


22 


THE  KAILWAY  LOCOMOTIVE 


which  is  a  modification  of  Mr.  Ivatt's  on  the  Great  Northern. 
Swing  links  are  employed  to  give  traverse.  Fig.  28  illustrates 
this  bogie  as  fitted  to  Mr.  Churchward's  latest  design,  the  four- 
cylinder  simple  engines  of  the  Star  class  working  the  heavy 
long-run  West  of  England  express.  A  strong  casting  A,  closely 
resembling  an  old  Greek  seat  or  stool,  with  four  curved  legs,  of 
which  two  are  shown  by  B  B,  is  bolted  to  the  front  end  of  the 
engine  and  drops  down  between  the  bogie  frames.  Four  links  C 
unite  A  with  the  bogie.  So  far  we  have  the  ordinary  swing  link. 
The  difference  lies  in  the  use  of  double  suspension  pins  D  D, 


FIG.  28. — Swing  link  bogie,  Great  Western  Eailway. 

one  in  each  of  the  elongated  holes.  On  the  straight  the  engine 
is  carried  on  both  pins.  When  a  curve  is  taken  the  lower  end 
of  C  is  swung  on  a  curve  to  the  right  or  left.  The  link  then 
leaves  one  pin  and  is  carried  only  by  the  other.  The  condition 
is  then  one  of  unstable  equilibrium,  and  the  front  end  of  the 
engine  being  raised  it  tends  to  fall  and  restore  the  link  to  a 
bearing  on  both  pins  D  D.  The  Great  Western  bogie  is  fitted 
with  the  vacuum  brake,  the  mechanism  for  which  crowds  all  the 
available  space,  and  this  arrangement  is  found  more  convenient 
than  the  two  inclined  links  of  the  Great  Northern.  The  pins 
D  D  run  fore  and  aft  between  two  cross  beams  uniting  the  two 
side  frames  of  the  bogie. 


BOGIES  23 

Three  typical  bogies  have  now  been  illustrated.  Those  used 
on  other  railways  only  differ  from  these  in  details,  as,  for  example, 
the  use  of  coiled  or  leaf  traverse  springs  instead  of  indiarubber 
pads. 

Reference  must  be  made  here  to  a  very  noteworthy  express 
locomotive  designed  by  the  late  Patrick  Stirling  while  locomotive 
superintendent  of  the  Great  Northern  Railway,  about  1872,  which 
represented  an  exception.  A  number  of  engines  built  to  this 
design  carried  on  the  express  traffic  of  the  line  for  several  years 
with  the  utmost  success,  until,  indeed,  they  were  overcome  by 
the  increasing  weight  of  the  trains  which  they  were  called  upon 
to  haul.  They  had  "  single  "  driving  wheels — that  is,  only  one 
pair— 8  feet  1  inch  in  diameter,  with  new  tires,  and  outside 
cylinders  18  inches  diameter  by  28  inches  stroke — at  the  time 
probably  the  largest  locomotive  cylinders  in  the  world,  certainly 
the  largest  in  Great  Britain.  A  pair  of  trailing  wheels  4  feet 
1  inch  in  diameter  was  placed  under  the  footplate.  The  leading 
end  of  the  engine  was  carried  on  a  four-wheeled  bogie,  with 
wheels  3  feet  11  inches  in  diameter  and  (j  feet  6  inches  between 
the  axles.  This  bogie  was  altogether  remarkable  and  excellent- 
It  had  no  traversing  arrangement ;  no  springs  to  restore  it  to  the 
normal ;  no  complications  of  any  kind,  and  yet  it  did,  up  to  a 
certain  point,  all  that  the  most  complex  bogie  can  do.  It 
swivelled  on  a  pin  like  other  bogies,  but  this  pin  was  not  put  in 
the  centre  of  its  length,  but  6  inches  nearer  to  the  hind  than  the 
front  axle.  If  the  pin  had  been  placed  in  the  centre  of  the  length 
of  the  bogie  then  the  leading  wheels  could  not  follow  the  curve, 
because  the  leading  end  of  the  engine  would  pull  the  whole  bogie 
outward.  As,  however,  the  pin  was  placed  far  back,  then  the 
centre  point  in  the  length  of  the  bogie  could  move  inwards,  which 
is  precisely  what  the  traversing  gear  already  described  is  intended 
to  permit,  and  the  moment  the  curve  had  been  traversed  the 
bogie  would  automatically  set  itself  normal  to  the  road.  For 
very  sharp  curves  the  amount  of  traverse  which  can  be  had  in 
this  way  is,  however,  not  sufficient,  but  on  the  Great  Northern 
these  engines  ran  with  a  minimum  of  resistance.  D.  K.  Clark, 
writing  of  them,  says :  "  The  bogie  leads  better  in  having  the 


24 


THE  RAILWAY  LOCOMOTIVE 


Cast  iron  blocks'  T'tmmis  Spring  put 
in  place  of  with  a 
compression  of  5cwl. 


EiG.  29. — Traversing  leading  axle,  Lancashire  and  Yorkshire  Railway. 


BOGIES  25 

leading  wheels  better  in  advance  than  if  the  pivot  were  equi- 
distant between  the  axles.  Not  only  do  the  leading  wheels  turn 
to  the  curve  with  greater  facility,  but  the  hind  bogie  wheels  make 
less  transversal  movement  towards  the  outer  rail,  and  in  so  much 
the  guiding  of  the  engine  is  eased." 

The  place  of  the  bogie  is  in  some  cases  taken  by  the  traversing 
axle  box,  which  has  assumed  several  forms.  One  of  the  best  was 
that  invented  by  the  late  W.  Bridges  Adams,  and  successfully 
used  on  many  railways,  among  others  the  London,  Chatham  and 

b* 


i_.. 


FIG.  30. — Mr.  Baldry's  rule  for  finding  the  centre  from  which 
to  strike  the  curve  of  a  radial  axle  box. 

Dover,  and  the  Metropolitan  extension.  Fig.  29  illustrates  a 
traversing  leading  axle  as  used  now  on  the  Lancashire  and  York- 
shire Kailway.  The  axle  C  is  enclosed  in  a  curved  casing  or 
inverted  trough  A,  which  carries  at  each  end  the  axle  box.  The 
spring  strut  is  shown  by  D.  Its  lower  end  drops  into  a  brass 
foot  or  pedestal  which  rests  on  the  flat  top  of  the  axle  box,  which 
moves  under  it  as  the  engine  takes  a  curve.  A  is  in  the  same 
way  enclosed  in  a  trough  B,  which  is  part  of  the  cross  framing  of 
the  engine  under  the  smoke  box.  Suitable  guiding  faces  are 
provided  on  and  in  the  two  troughs ;  consequently  the  leading 
wheels  can  move  freely  right  and  left  in  a  curve  the  length  of  the 
radius  of  which  is  that  of  the  curve  of  B.  To  regulate  and 


26  THE   RAILWAY  LOCOMOTIVE 

control  the  amount  of  the  traverse,  and  to  supply  the  necessary 
effort  required,  as  just  explained,  to  get  the  engine  round  a  curve, 
a  species  of  box  E  is  fitted  on  the  lower  part  of  B,  so  as  to  clear 
the  axle.  In  this  is  placed  a  coiled  spring.  Through  the  spring  is 
passed  a  bolt  G,  the  ends  of  which  are  secured,  as  shown,  to  cross 
heads  H  H  bolted,  as  shown,  to  A.  Cast  iron  blocks  are  placed 
at  each  end  of  the  coiled  spring,  and  on  these  it  bears.  Brass 
ferrules  F  F  are  interposed  at  each  end,  between  the  cast  iron 
block  and  the  cross  head.  The  spring  is  put  in  with  some  initial 
compression.  If  now  the  axle  traverses,  the  ferrule  at  one  end 
will  be  pushed  in  with  the  cast  iron  block  away  from  I,  and  the 
coiled  spring  will  be  compressed.  Of  course  the  same  thing 
occurs  in  reverse  order  if  the  curve  is  reversed.  This  arrange- 
ment is  typical  of  many  others — in  all  the  principle  is  the  same, 
the  difference  is  in  details.  The  rule  for  finding  the  centre  from 
which  the  curve  of  the  axle  casing  is  struck  is  given  by  Mr. 
Baldry ;  x  is  the  length  of  the  radius  wanted.  The  diagram, 
Fig.  30,  explains  itself. 


CHAPTEK   III 

THE    ACTION    OF    THE    BOGIE 

LEAVING  now  the  construction  of  the  bogie,  let  us  consider  what 
it  does,  how  it  behaves  on  the  road,  its  merits  and  demerits. 

In  theory  the  bogie  facilitates  the  movement  of  an  engine 
round  a  curve.  The  entire  weight  of  the  leading  end  of  the 
engine  is  distributed  over  four  wheels  instead  of  two,  and  the 
bogie's  action  is  to  consolidate  the  track  by  sending  the  sleepers 
down  to  their  bearings  on  the  ballast  in  advance  of  the  driving 
wheels.  All  this  is  meritorious  to  a  very  high  degree ;  and  it 
has  been  plainly  stated  that  the  bogie  greatly  reduces  the 
chance  of  derailment,  and  indeed  enables  curves  to  be  traversed 
which  without  its  aid  would  be  quite  inadmissible.  So  long  as 
speeds  are  moderate  all  these  propositions  may  be  accepted  as 
true. 

It  is,  however,  a  fact  worth  notice  that  in  former  years  derail- 
ments seldom  occurred  with  serious  results.  The  cause  of  them 
was  almost  invariably  obvious.  A  rail  was  broken  or  the  ballast 
was  defective,  or  points  were  wrongly  set.  The  worst  accidents 
were  collisions.  In  the  present  day  the  worst  accidents  are  due 
to  derailment,  and  in  notable  instances  no  satisfactory  explanation 
has  been  forthcoming  to  account  for  the  engine  leaving  the  rails. 
There  are  large  numbers  of  locomotives  still  running  which  have 
not  bogies ;  they  appear  to  be  exempt  from  mysterious  derail- 
ment.1 Under  the  circumstances  it  is  not  unfair  to  say  that  the 

1  It  is  right  to  say  here  that  many  engineers  maintain  that  there  are  no 
such  things  as  mysterious  derailments,  and  that  in  far  the  greater  number 
of  cases  when  an  engine  leaves  the  rails  the  fault  lies  in  the  permanent  way 
and  not  in  the  engine.  The  whole  subject  is  dealt  with  statistically  further 
on. 


28  THE  EAILWAY  LOCOMOTIVE 

excellence  of  the  bogie  is  open  to  question.  We  shall  see 
presently,  when  we  come  to  consider  the  internal  disturbing  forces 
of  a  locomotive,  how  these  affect  the  bogie.  For  the  moment  we 
must  confine  our  attention  to  the  external  forces.  We  have  seen 
that  these  are  of  two  kinds,  vertical  and  horizontal.  Of  course 
it  is  obvious  that  various  combinations  of  both  can  take  place. 
The  first  is  due  to  the  absence  of  uniform  level  in  the  rails. 
However  carefully  the  platelayer  may  attend  to  packing  up  the 
sleepers,  the  road  always  sinks  under  the  tread  of  an  engine,  and 
rises  again  when  it  has  passed  ;  the  amount  of  sinking  is  a 
variable  quantity.  Again,  the  rails  spring  between  the  sleepers 
under  the  tread  of  the  engine.  The  rail  tables  are  not  dead  true. 
The  result  of  all  this  is  that,  as  has  already  been  said,  the  loco- 
motive continually  moves  on  a  road  full  of  waves  of  varying 
altitudes  and  lengths.  It  is  true  that  they  are  very  small  waves. 
It  is  none  the  less  certain  that  they  make  themselves  felt — how 
much  felt  the  traveller  in  a  luxurious  carriage  little  knows.  A 
full  appreciation  of  the  good  and  bad  qualities  of  the  permanent 
way  of  any  railway  can  only  be  got  by  standing  on  the  footplate 
of  a  locomotive  for  a  couple  of  hours  while  it  runs  at  various 
speeds. 

In  by  far  the  larger  number  of  locomotives  the  entire  weight 
of  the  leading  end  of  the  engine,  say  sixteen  tons,  is  carried  on  a 
bolster  crossing  the  bogie  frame,  in  such  a  way  that  it  acts  at 
the  centre  of  the  bogie  frame  only.  Each  of  the  four  corners  of 
the  bogie  will  represent  four  tons,  and  that — less  the  weight  of 
the  wheels  and  springs — is  the  weight  pressing  down  each  axle 
box  on  the  journal.  This  load  is  transmitted  outwards  from  the 
fore  and  aft  centre  line  of  the  locomotive.  There  is  nothing 
whatever,  so  far,  to  prevent  any  one  corner  of  the  bogie  from 
rising  or  falling.  If  the  right-hand  leading  wheel  goes  down  half 
an  inch,  the  centre  of  the  leading  end  of  the  engine  bearing  on 
the  bogie  bolster  would  fall  half  as  much,  and  so  on.  The 
behaviour  of  a  four-wheeled  bogie  on  the  road  is  very  interesting. 
As  fitted  to  passenger  coaches  nothing  is  easier  than  to  watch  it 
when  two  suburban  trains  run  side  by  side.  As  a  rule  a  leafed 
spring  is  fitted  over  each  axle  box.  It  will  be  seen,  however,  that 


OF  ' 
UNIVERSITY 

OF 

THE  ACTION   OF  THE  BOGIE  29 

these  springs  never  bend.  The  bogie  is  continually  on  the  jump 
as  a  whole,  wheels  and  all,  but  it  plays  about  the  centre  pivot. 
The  axle-box  springs  are  of  no  use;  and,  indeed,  some  bogies  are 
made  without  them,  elasticity  being  obtained  by  the  springs 
between  the  cross  bolsters  of  the  carriage  frame  and  the  bogie  near 
the  centre.  It  has  never  been  disputed  tbat  the  ease  with  which 
all  the  four  wheels  take  the  same  load  and  transmit  it  to  the  rail  is 
an  excellent  thing.  Bogies  relieve  the  stress  on  the  permanent 
way,  and  for  that  reason  are  in  favour  with  the  civil  engineering 
staff  of  railways  ;  but  it  will  not  do  to  forget  that  this  very 
freedom  of  motion  may  be  a  direct  source  of  danger.  It  will  not 
do  to  leave  the  leading  end  of  the  engine  to  wander  from  side  to 
side.  The  bogie  itself,  too,  is  liable  to  "  get  across  the  road." 
Its  wheel  base  is  short,  and  unless  special  precautions  are  taken 
it  may  "  wobble  " — there  is  no  better  word — as  it  runs,  and  the 
wobbling  may  throw  the  flanges  of  the  wheels  to  the  right  and 
left  alternately  with  such  violence  that  the  wheel  may  escape 
from  the  rails.  Many  engineers,  therefore,  insist  that  the  wheel 
base  of  a  four-wheeled  bogie  shall  be  made  at  least  half  as  long 
again  as  the  gauge  is  wide.  In  this  country  and  in  the  United 
States  6  feet  is  a  very  usual  wheel  base,  but  on  the  Continent, 
and  notably  in  Austria,  a  wheel  base  of  as  much  as  9  feet  is 
favoured. 

It  is  right  at  this  point  to  bring  a  fact  into  prominence  which 
is  frequently  overlooked — it  is  that  all  the  principal  parts  of  a 
locomotive  possess  a  great  deal  of  mass  ;  in  popular  phrase,  they 
are  very  heavy.  Mass  is  the  complement  of  momentum,  and 
the  stresses  set  up  in  starting  and  stopping  motion  are  corre- 
spondingly severe.  Thus,  if  from  any  cause,  such  as  crossing 
points,  &c.,  the  leading  or  trailing  end  of  a  bogie  is  violently 
flung  right  or  left,  although  the  distance  traversed  may  not 
exceed  three-quarters  of  an  inch,  yet  there  will  be  quite  momen- 
tum enough  to  cause  a  jerk  and  a  recoil,  and  it  may  easily  happen 
that  a  very  free  and  easy  bogie  may  give  a  very  unsteady,  lurch- 
ing engine  at  high  speed. 

Hitherto  we  have  been  considering  the  behaviour  of  a  bogie  on 
a  straight  line.  We  have  now  to  consider  the  behaviour  of  the 


30  THE  EAILWAY  LOCOMOTIVE 

bogie  on  a  curve,  a  thing  of  the  utmost  interest  in  its  relation  to 
the  rest  of  the  locomotive.  The  modern  bogie  is  always,  as  we 
have  seen,  permitted  to  traverse  under  the  engine.  If  the  bogie 
is  quite  free  to  traverse  across  the  engine  it  is  clear  that  it  can 
do  nothing  to  guide  the  engine  round  a  curve.  That  duty  would 
then  devolve  on  the  driving  wheels,  or  at  all  events  on  the  wheels 
next  behind  the  bogie.  But  the  bogie  is  never  quite  free.  It  is 
always  returned  to  the  central  position  by  inclined  planes,  swing 
links,  or  springs  shown  in  the  illustrations.  A  compromise  is, 
in  short,  effected  between  perfect  freedom  of  traverse  and 
absolute  restraint  of  lateral  motion  ;  and  the  result  is  that  the 
bogie  guides  the  leading  end  of  the  engine  round  curves.  To  do 
this  requires  an  effort,  the  amount  of  which  varies  as  the  square 
of  the  speed  and  the  radius  of  curvature.  In  popular  language, 
the  bogie  has  to  overcome  the  centrifugal  force  acting  on  the 
engine.  Inasmuch  as  a  good  deal  of  confusion  of  thought 
exists  about  all  this,  even  among  very  well  informed  persons,  it 
is  necessary  here  to  go  into  some  explanatory  details. 

It  is  an  axiom  of  dynamics  that  a  body  moving  freely  in  space 
under  the  action  of  a  single  force  will  describe  a  straight  line. 
If  it  is  to  describe  a  curve  of  any  order  another  force  or  forces 
must  also  act  upon  it.  An  engine  traversing  a  curve  does  not 
want  to  fly  outward,  but  to  move  straight  on.  It  is  not  that  the 
engine  would  leave  the  line,  but  that  the  line  leaves  the  engine. 
The  effort  of  the  engine  is  to  pursue  a  straight  course  which  is 
always  a  tangent  to  the  curve ;  there  is  no  effort  at  radial 
departure  made  by  the  engine.1 

The  bogie  then  must  keep  on  sluing  the  leading  end  of  the 
engine  round  the  curve,  while  the  trailing  end  is  similarly  worked 
on  by  the  other  wheels.  To  calculate  the  centrifugal  effort  of 
every  portion  of  a  locomotive  on  a  curve  would  be  a  tedious  and 
a  profitless  task.  In  practice  the  whole  "mass"  of  the  engine 

1  It  is  for  this  reason  that  a  locomotive  running  at  speed  is  never  derailed 
radially.  It  runs  off  the  line  obliquely,  and  in  many  instances  a  derailed 
engine  has  continued  its  course  for  several  yards  along  the  sleepers  quite 
close  to  the  rails.  This  is  just  what  might  be  supposed  to  happen  if  by  any 
agency  the  rails  were  suddenly  pulled  away  to  one  side  from  beneath  the 
wheels. 


THE  ACTION   OF   THE  BOGIE  31 

is  supposed  to  be  concentrated  at  the  centre  of  gravity,  and  the 
centrifugal  stress  can  be  determined  by  a  very  simple  calculation, 

C  =  Q0.0  p.    Here  C  is  the  centrifugal  effort  which  must  be  over- 

d2*J   -TAi 

come  to  make  the  engine  follow  the  curve,  W  is  the  weight  of  the 
engine,  V2  its  velocity  in  feet  per  second,  K  the  radius  in  feet 
of  the  curve.  In  other  words,  the  effort  required  to  keep  the 
engine  moving  round  the  curve  is  equal  to  its  weight  multiplied 
by  the  square  of  the  velocity  and  divided  by  32*2  times  the  radius 
of  the  circle  of  which  the  curve  forms  a  part. 

Let  us  suppose  that  the  curve  has  a  radius  of  600  feet,  and 
that  the  engine  is  running  at  thirty  miles  an  hour,  or  44  feet  per 
second,  and  its  weight  is  fifty  tons.  Then  the  effort  required  to 
keep  it  on  the  rails  and  prevent  it  from  flying  off  at  a  tangent 
will  be  approximately  five  tons.  If  the  speed  were  sixty  miles 
an  hour  then  the  necessary  centripetal  effort  would  be  twenty 
tons,  and  so  on.  Now  the  effort  must  be  distributed  among  the 
wheels,  and  only  those  whose  flanges  can  get  access  to  the  rails 
can  take  it  up.  It  may  easily  happen  that  the  distribution  is  not 
uniform.  Thus,  if  an  engine  is  fitted  with  six  wheels  and  a  four- 
wheeled  bogie,  both  the  bogie-wheel  flanges  resting  against  the 
inner  side  of  the  outer  rail  will  act.  So  will  the  first  and  last 
wheel  of  the  six  wheels,  but  the  middle-wheel  flange  cannot  touch 
the  outer  rail  unless  one  or  both  of  the  other  two  are  fitted  with 
a  traversing  arrangement  or  its  equivalent,  such  as  a  blind  tire. 
It  will  be  seen  that  while  "blinding"  tires  gives  freedom  of 
motion  round  a  curve  it  also  augments  the  stress  on  the  flanged 
wheels. 

Although  it  simplifies  calculations  to  refer  the  whole  effort  to 
the  centre  of  gravity  of  a  locomotive,  really  the  stresses  are 
distributed  about  it  in  a  very  complicated  way  impossible  to 
follow  as  a  whole.  Thus,  for  example,  we  have  to  keep  in  mind 
that  the  complete  engine  has  not  only  to  get  round  the  curve, 
but  that  it  is  also  continually  rotating  round  its  own  longitudinal 
centre  of  gravity.  Very  complicated  mathematics  are  involved, 
and  the  result  after  all  is  fortunately  not  needed.  The  general 
rule  to  be  observed  is  that  as  many  wheels  as  possible  shall  act 


32  THE   EAILWAY  LOCOMOTIVE 

on  the  outside  rail  to  resist  the  tangential  effort  of  the  engine  to 
leave  the  line.  It  is,  however,  often  assumed  that  if  the  leading 
wheels  radiate  to  the  curve,  the  engine  will  follow  just  as  a 
motor  car  does  when  steered  to  right  or  left ;  but  the  analogy  is 
far  from  perfect,  because  first,  in  the  motor  car,  there  is  only  one 
pair  of  wheels  to  follow  the  lead,  and  the  differential  gear  permits 
the  outer  wheel  to  move  just  as  much  faster  than  the  inner  wheel 
as  corresponds  to  the  extra  distance  which  it  has  to  pass  over ; 
but  besides  this,  the  motor  car  is  subjected  to  centrifugal  effort 
just  as  the  locomotive  is,  and  the  effort  may  suffice  to  skid  the 
car  across  the  road,  producing  side  slip  which  is  the  analogue  of 
derailment. 


CHAPTEE  IV 

CENTRE    OF    GRAVITY 

So  far,  although  the  subject  has  been  treated  as  though  the 
whole  effort  has  been  concentrated  on  the  centre  of  gravity  of  the 
engine,  nothing  has  been  said  concerning  the  position  of  that 
centre.  For  anything  to  the  contrary  it  might  be  at  the  rail 
level,  and  the  outward  thrust  of  five  tons  named  above  might  be 
supposed  to  be  exerted  directly  on  the  inside  of  the. rail.  In 
point  of  fact  the  conditions  lack  this  simplicity.  The  vertical 
centre  of  gravity  is  somewhere  between  4  feet  and  5  feet  above 
the  rails,  according  to  the  design  of  the  engine.  The  centrifugal 
effort  consequently  tends  not  only  to  make  the  engine  leave  the 
rails,  but  to  upset  it.  Overturning  will  take  place,  if  at  all,  on  the 
outer  rail  as  a  pivot,  and  complete  upsetting  cannot  occur  until 
a  vertical  line  drawn  through  the  centre  of  gravity  falls  outside 
the  rail.  Regard  the  triangle  C  E  F,  Fig.  31,  as  a  solid  block 
standing  on  a  table.  Then  C  represents  the  base,  on  the  width 
of  which,  as  compared  with  the  height,  the  stability  of  the  triangle 
depends. 

At  one  period  in  the  history  of  the  locomotive  it  was  held  to 
be  good  to  keep  the  centre  of  gravity  low,  because  upsetting  was 
feared ;  but  it  has  long  been  recognised  that  while  the  chances 
of  an  engine  overturning  are  very  few,  a  rise  in  the  centre 
of  gravity  confers  substantial  advances,  which  may  now  be 
considered. 

In  the  diagram,  Fig.  31,  let  the  arrow  A  indicate  the  centri- 
fugal effort  supposed  to  be  concentrated  at  the  rail  level.  Let 
this  effort  be  represented  by  screw  jacks,  A  and  D,  laid  on  their 
sides,  one  for  each  wheel,  tending  to  force  it  off  the  rail.  The 
resistance  to  derailment  will  then  be  measured  by  the  stress  with 

R.L.  -  D 


34 


THE  EAILWAY  LOCOMOTIVE 


which  the  wheel  presses  down  on  the  rails  due  to  gravity1  and 
it  will  be  resisted  by  the  chairs  and  keys  supporting  the  outer 
rail,  B. 

Next  let  the  screw  jacks,  as  represented  by  the  arrow  D,  act 
at  a  level  4  feet  6  inches  above  the  rail ;  we  then  have,  instead  of 
a  single  stress,  two.  The  first  as  before  horizontal,  and  the 
second  exerted  along  the  inclined  line  E.  It  is  easy  to  see  that, 
by  the  ordinary  laws  of  the  composition  and  resolution  of  forces, 
the  whole  derailing  effort  is  concentrated  along  the  line  E.  The 


FIG.  31.— Centrifugal  effort. 

result  is  that  the  load  on  the  outside  wheel  is  much  increased, 
that  on  the  inside  wheel  much  diminished.  The  effort  to  burst 
the  track  is  reduced,  and  the  resistance  to  derailment  augmented. 
But  it  must  not  be  forgotten  that  while  the  chances  of  derailment 
are  minimised  the  risk  of  overturning  is  increased.  Mr.  John 
Audley  Aspinall,  while  chief  mechanical  engineer  of  the  Lanca- 
shire and  Yorkshire  Kailway,  of  which  line  he  has  been  general 
manager  for  some  years,  in  the  course  of  a  report  on  the 

1  In  the  sense  that  the  greater  the  weight,  the  greater  the  effort  required 
to  force  the  flange  over  the  rail. 


CENTEE   OF   GEAVITY  35 

type  of  locomotive  most  suitable  for  high  speed,  presented 
to  the  International  Kailway  Conference  some  ten  years  ago, 
wrote :  "  The  oscillations  of  an  engine  with  a  high  centre  of 
gravity  will  be  longer  than  those  of  a  low  engine.  It  will 
also  ride  easier,  owing  to  the  elasticity  of  the  springs  being 
brought  more  into  play.  This  is  also  conducive  to  the 
reduction  of  side  shocks  and  the  stresses  in  the  wheels  and 
axles  are  minimised.  It  must  not,  however,  be  overlooked  that 
the  higher  centre  of  gravity,  when  passing  round  a  curve,  causes 
the  load  on  the  inner  rail  to  be  diminished,  and  as  the  front 
end  of  the  engine  is  liable  at  any  time  to  be  thrown  violently 
to  the  inside  it  will  have  a  tendency  to  leave  the  road  if  the 
super-elevation  of  the  outer  rail  is  excessive.  The  effect  produced 
by  raising  the  centre  of  gravity  will  be  readily  understood  if  the 
reader  will  compare  No.  1  and  No.  2  and  the  relation  which  C 
bears  to  E  in  each." 

Other  things  being  equal,  the  lower  the  centre  of  gravhVy 
the  greater  the  chance  of  derailment  due  to  centrifugal  effort, 
and  the  less  the  chance  of  overturning,  and  vice  versa.  Now  in 
practice  curves  traversed  on  main  lines  at  high  speeds  have 
radii  so  great  that  the  chance  of  overturning  is  very  small, 
and  a  high  centre  of  gravity  gives  an  engine  which  runs  easily 
and  does  not  stress  the  road  sideways.  The  reason  is  that 
the  vertical  component  of  the  centrifugal  effort  tends  as  shown 
to  compress  the  outer  and  relax  the  inner  springs.  In  other 
words,  if  the  derailing  effort  were  concentrated  at  the  rail  level, 
there  would  be  no  resilient  resistance  offered  to  it ;  but  the 
elevation  of  the  locus  of  effort  bringing  the  springs  into  play  eases 
the  movement  round  the  curve.  For  the  mere  purpose  of 
explanation  or  calculation  it  is  assumed  that  every  portion  of 
the  engine  traverses  a  true  curve  in  a  determinate  circular  path. 
In  practice,  however,  this  is  very  far  from  being  the  truth.  A 
locomotive  always  gets  round  a  curve  in  a  series  of  jerks,  so  to 
speak.  It  is  as  though  the  permanent  way  represented  a 
polygonal  instead  of  a  circular  path.  Why  this  should  be, 
and  the  influence  of  small  matters  of  detail  in  design  and 
construction,  must  now  be  explained.  To  do  this  it  is  necessary 

D2 


36  THE   RAILWAY  LOCOMOTIVE 

to  consider  the  effect  of  an  expedient  universally  adopted  to 
add  to  the  safety  and  improve  the  running  of  railway  vehicles 
round  curves.  The  outer  rail  is  raised  above  the  level  of  the 
inside  rail,  the  amount  of  super-elevation  is  given  by  the 

V2 
formula  E  =  W  .    Here  E  is  the  super-elevation  in  inches, 

1*^5    -LV 

W  the  gauge  in  feet,  V  the  velocity  in  miles  per  hour,  and  R 
the  radius  of  the  curve  in  feet.  For  moderate  curves  plate- 
layers work  to  a  rule  which  is  sufficiently  exact  for  ordinary 
railway  practice.  They  stretch  a  66  feet  tape  as  a  chord  of  the 
curve,  and  then  measure  the  distance  between  the  tape  and 
the  rail  at  33  feet ;  that  distance  is  the  super-elevation.  The 
purpose  served  is  precisely  that  with  which  a  cyclist  turning 
a  corner  or  racing  round  a  circular  track  inclines  inwards. 
Racing  tracks  are  indeed  very  steeply  inclined  when  the  turns 
are  sharp.  Unfortunately  the  super-elevation  that  is  suitable 
for  one  speed  must  be  too  great  for  a  lower  speed,  and  too 
little  for  a  higher  speed,  and  that  not  only  as  the  speed,  but 
as  the  square  of  the  speeds.  In  practice  the  super-elevation 
is  "  jimmered" — that  is  to  say,  a  compromise  is  arrived  at,  the 
tendency  being  to  make  the  super-elevation  too  great.  So  far 
nothing  has  been  said  about  wheels.  They  will  be  more  fully  con- 
sidered presently.  For  the  moment  it  is  enough  to  say  that  when 
tires  are  new  they  are  slightly  conical.  The  inclination  is  usually 
one  in  twenty.  The  object  is  to  keep  the  flanges  away  from  the 
road  as  much  as  possible.  Let  us  suppose  that  the  difference  in 
the  inner  and  outer  diameter  of  a  6-foot  wheel  is  0*4  inch,  then 
the  circumference  will  be  a  little  over  1  inch  greater  inside, 
next  the  flange,  than  outside,  and  the  difference  between  the 
two  circumferences  will  be  about  2  inches.  The  outside  wheel 
on  the  curve  therefore  has  a  longer  distance  to  traverse  per 
revolution  than  the  inside  wheel,  and  this  of  course  tends  to 
compensate  for  the  trouble  due  to  the  wheels  being  rigidly 
secured  to  the  axles,  but  in  practice  we  find  that,  thanks  to  the 
super-elevation  and  the  coning,  the  wheels  continually  slip 
across  the  rail  tops,  moving  outwards  and  then  inwards.  In 
a  word  the  whole  traverse  of  a  curve  is  always  effected,  as  stated 


CENTEE   OF   GRAVITY  37 

above,  in  a  series  of  jerks,  the  violence  of  which  depends  on  the 
condition  of  the  road,  of  the  tires,  of  the  axle  boxes  and  springs, 
and  of  the  good  or  bad  qualities  of  the  design.  In  some  cases 
the  engine  "rides"  like  a  coach,  the  slipping  being  almost 
imperceptible,  in  others  the  action  is  very  disagreeable  and 
injurious  to  the  track. 

One  more  adverse  influence  has  to  be  explained,  that  is 
to  say  lurching  or  rolling.  It  can  best  be  illustrated  by  a 
practical  test.  If  the  reader  will  stand  on  a  railway  platform 
and  watch  an  engine  coming  towards  him  at  speed  he  will 
see  at  once  what  takes  place.  Indeed,  if  the  road  be  not  in 
perfect  order  and  the  engine  well  designed,  he  may  now  and 
then  feel  a  little  surprise  that  derailment  does  not  take  place. 
But  the  essential  condition  of  safety  is  that  the  wheels  should  not 
lift  off  the  rails.  The  rolling  and  jerking  and  pitching  all  take 
place,  be  it  remembered,  above  the  wheels.  These  last  are  always 
practically,  at  least  in  so  far  as  all  but  the  drivers  are  concerned, 
in  contact  with  the  rails.  The  movements  of  the  engine  above 
them  are  at  once  controlled  by  the  springs  and  due  to  them, 
and  therefore  the  "  springing  "  of  an  engine  is  a  very  nice 
question  of  design,  as  on  it  a  great  deal  depends.  Diversities  of 
opinion  exist  as  to  the  amount  of  resilience  permissible.  The 
maximum  range  of  motion  allowed  in  an  axle  box  in  this  country 
is,  as  has  already  been  stated,  about  2  inches  ;  abroad  it  is  almost 
always  3  inches,  not  infrequently  4  inches.  But  balance  beams 
or  compensating  levers  profoundly  affect  the  range. 

So  far  we  have  confined  our  attention  to  the  engine  only,  but 
the  engine  when  at  work  is  either  coupled  to  a  tender  or  a  train. 
In  the  former  case,  two  buffer  heads,  actuated  by  a  powerful 
cross  spring  or  two  helical  springs  under  the  tender,  rest 
against  the  transverse  hindermost  plate  of  the  engine  framing. 
The  tie  bar  between  the  engine  and  tender  is  secured  by  a  pin 
dropped  into  eyes  in  a  casting  under  the  footplate  provided  for 
them.  The  result  is  that  the  engine  and  tender  resist  lateral 
bending  effort,  and  so  the  stress  when  passing  round  a  curve 
is  increased.  The  same  thing  happens  when  a  tank  engine  is 
tightly  coupled  to  a  train. 


38  THE  EAILWAY  LOCOMOTIVE 

A  review  of  all  the  conditions  shows  that  a  locomotive  engine 
and  tender  are  specially  contrived  to  run  straight  on  straight 
roads ;  and  that  although  devices  are  provided  to  permit  the 
lateral  flexure  required  to  traverse  a  curve,  yet  that  all  these  are, 
regarded  from  one  point  of  view,  of  a  nature  to  favour  derailment, 
and  that  so  powerfully  that  a  mistake  might  easily  render  it 
impossible  for  a  locomotive  to  traverse  curves  of  even  great  radii 
without  risk.  Thus,  for  example,  a  long  six- wheeled  engine  tight 
to  gauge  could  not  get  round  if  the  controlling  springs  of  a 
traversing  axle  were  too  stiff  and  unyielding.  It  may  be  added 
that  the  conditions  are  so  variable  and  complicated  that  minute 
calculation  is  set  at  defiance,  and  the  lateral  resistance  put  in  is 
settled  by  the  results  of  experience,  and  it  is  never  made  greater 
than  will  just  suffice  to  meet  the  conditions. 

Before  leaving  this  section  of  our  subject  it  is  worth  while 
briefly  recalling  to  the  reader's  notice  a  few  important  facts.  In 
the  first  place,  as  has  been  already  set  forth  in  Chapter  I.,  if  a  rail- 
way were  absolutely  level  and  smooth,  and  the  wheels  truly 
cylindrical,  springs  and  bogies  would  not  be  needed.  At  the 
most,  indeed,  india-rubber  blocks  interposed  between  the  axle 
boxes  and  frames  to  deaden  vibration  could  satisfy  all  the 
vehicular  conditions.  Secondly,  the  railway  of  reality  is  curved. 
It  is  not  level  and  it  is  not  smooth.  The  task  of  the  designers 
and  builders  of  locomotives  is  not  only  to  produce  a  machine 
which  can  pull  a  train,  but  to  reduce  to  the  lowest  possible  point 
the  effects  of  the  external  disturbing  agencies  due  to  the  imper- 
fections in  the  road.  It  is  not  enough  in  getting  out  a  design  to 
put  in  sufficient  boiler  power,  an  excellent  engine,  and  so  on. 
The  locomotive  as  a  machine  which  has  to  traverse  an  imperfect 
road  at  a  very  high  speed  is  a  much  more  important  considera- 
tion. It  will  not  do  to  say  of  a  given  engine  that  it  is  more 
economical  of  fuel  than  any  other  on  a  given  line,  if  it  is  feared 
that  it  will  run  off  the  track  if  driven  at  more  than  50  miles  an 
hour.  This,  it  may  be  added,  is  in  no  way  a  fancy  picture ; 
many  engines  of  the  kind  have  been  built.  Take,  as  an  example, 
the  Great  Liverpool,  a  very  powerful  engine  designed  by  the  late 
Mr.  Thomas  Crampton  many  years  ago.  The  engine  could  not 


CENTRE   OF   GRAVITY  39 

be  used  because  it  broke  the  rails.  In  the  present  day,  a  wide 
difference  exists  among  locomotives  doing  the  same  work  at  the 
same  speeds,  some  being  much  lighter  on  the  permanent  way  than 
others.  It  has  been  said  of  a  big  engine  that  "  she  never  got 
through  a  week  without  breaking  a  rail."  Too  much  stiffness, 
too  much  flexibility,  bad  springing,  bad  distribution  of  weight, 
and  various  other  factors  which  will  be  dealt  with  when  we  come 
to  consider  the  internal  disturbing  forces  of  a  locomotive 
contribute  to  the  unhappy  result. 


CHAPTEE  V 

WHEELS 

OBVIOUSLY,  the  wheels  of  a  vehicle  are  an  important  part  of  it. 
It  is  time  now  to  speak  in  some  detail  of  those  of  a  locomotive. 
In  the  earlier  history  of  locomotives  they  were  made  of  cast  iron, 
round  which  a  wrought  iron  tire  was  shrunk  on ;  the  tires  were 
rolled  in  straight  bars,  cut  off  in  lengths,  scarfed  at  the  ends, 
bent  into  rings  and  welded.  They  frequently  broke  at  the  weld. 
It  is  said  that  in  the  early  days  of  the  London  and  Birmingham 
Kailway  a  driver  of  an  up  train  at  night,  when  passing  Tring,  felt 
the  engine  jump,  but  nothing  more  happened  except  that  she  ran 
roughly  the  rest  of  the  trip  to  London.  On  going  round  with 
his  lamp  at  Chalk  Farm  he  found  that  one  of  the  driving-wheel 
tires  had  come  off.  The  journey  was  completed  on  the  wheel 
centre.  The  tire  was  found  in  the  ditch  next  day  near  Tring. 
Very  dreadful  accidents  have  resulted  from  broken  tires. 

Many  years  have  elapsed  since  a  method  of  producing  tires  of 
solid  steel  without  a  weld  was  invented,  and  tires  so  made  are 
invariably  used  now.  A  suitable  steel  billet  or  ingot  is  forged 
into  the  shape  of  a  cheese  under  a  heavy  steam  hammer. 
Through  the  centre  of  this  steel  cheese  a  succession  of  punches, 
larger  and  larger,  are  driven  until  the  cheese  has  become  a  very 
thick  ring.  This  is  heated  and  placed  on  the  beak  of  a  special 
anvil,  and  forged  out  until  it  is  perhaps  half  the  finished 
diameter,  and  is  then  put  on  to  the  central  vertical  roller  of  a 
very  powerful  machine. 

There  are  various  tire-rolling  machines  in  use.  It  will  suffice 
to  illustrate  one  of  the  latest  type,  which  is  made  by  Messrs. 
P.  E.  Jackson  &  Company,  Limited,  Salford,  Manchester.  In 
the  space  at  disposal  it  is  impossible  to  illustrate  the  details  of  a 


WHEELS 


41 


42  THE  EAILWAY  LOCOMOTIVE 

very  large  and  complex  machine  ;  only  the  outline  is  given  on 
page  41,  Fig.  32.  It  is  20  feet  6  inches  long  on  the  floor  line, 
and  about  15  feet  high  from  the  base.  The  tire,  whatever  its 
diameter,  is  laid  on  a  horizontal  circular  table  A.  The  tire  is 
first  roughed  out  between  the  two  rolls  to  the  section  marked  B ; 
then  the  table  is  raised  and  the  tire  is  passed  through  the 
grooves  C,  and  again  through  the  grooves  D,  and  so  finished. 
Described  more  in  detail,  these  mills  roll  tires  up  to  9  feet 
diameter.  The  tires  are  rolled  on  a  horizontal  table,  the  rolls 
being  vertical,  and  having  two  to  four  grooves  for  roughing  and 
finishing  the  tire  at  one  operation.  The  table  carrying  the  tire 
is  adjustable  vertically  to  suit  the  rolls.  This  adjustment  is 
quickly  made  through  a  hydraulic  cylinder  and  suitable  gearing. 
The  table  is  fitted  with  rolls  for  carrying  the  tires,  and  with  a 
movable  carriage  moved  back  by  the  tire  as  it  enlarges,  and 
carrying  a  top  roll,  assisting  to  keep  the  tire  true  ;  also  with  side 
rolls  working  on  slides.  A  very  sensitive  gauging  apparatus  is 
provided  for  indicating  the  size  of  tire,  the  pointer  and  index 
being  on  the  front  side  of  the  main  frame.  The  levers  and 
handles  are  also  on  the  same  side  and  placed  as  most  convenient 
for  use.  In  some  cases  the  main  or  large  roll  is  cast  complete 
and  the  grooves  turned  in  it,  the  roll  then  being  changed  for 
different  sections,  or,  as  is  now  more  general,  the  centre  of  the 
roll  is  a  forged  steel  shaft,  and  loose  rolls  for  the  various  sections 
are  put  on  it.  These  loose  rolls  are  readily  changed  for  the 
various  sections.  The  smaller  roll  working  inside  the  tire  is 
quickly  raised  and  lowered  by  a  hydraulic  cylinder.  The  large 
roll  moves  in  and  out  a  distance  of  21  inches,  allowing  for  the 
changing  of  the  loose  rolls  and  the  greatest  thicknesses  of  tire 
blooms.  The  roll  is  carried  by  bearings  at  top  and  bottom  on 
strong  slides  worked  by  screws  in  the  main  frame.  The  slides 
have  a  slow  speed  for  the  rolling  pressure  and  a  quick  speed  for 
bringing  the  rolls  up  to  the  work  and  for  reversing.  The  roll  is 
turned  by  a  large  bevel  wheel  at  the  foot,  driven  by  a  steel  bevel 
pinion  on  the  shaft  running  under  the  main  frame  to  the  driving 
wheels  at  the  engine. 

The  mill  consists  of  a  cast  iron  main  frame,  fitted  with  strong 


WHEELS  43 

slides  and  screws  for  moving  the  main  roll  shaft  in  and  out,  the 
slides  forming  the  bearings  for  the  roll.  The  main  frame  carries 
the  bearings  for  the  small  roll,  and  is  provided  with  a  bracket 
and  hydraulic  cylinder  for  lowering  and  raising  this  roll  in  and 
out  of  the  tires.  The  frame  also  carries  a  double  cylinder  engine, 
8-inch  cylinders  with  quick  spur  gear  and  slow  worm  gear  for 
working  the  slides  (carrying  the  roll  shaft)  in  and  out.  The  roll 
shafts  are  of  steel,  the  shaft  for  the  large  or  main  roll,  i.e.,  the 
roll  working  on  the  outside  of  the  tire,  being  13  inches  in 
diameter  at  the  bottom  bearing,  and  it  can  be  made  up  to 
11  inches  diameter  of  top  bearing.  The  shaft  for  the  smaller 
roll,  i.e.,  the  roll  working  on  the  inside  of  the  tire,  can  be  made 
up  to  11  inches  diameter  in  the  top  bearing.  The  large  roll 
shaft  is  also  supported  on  a  cast  iron  sliding  footstep  and  stand, 
and  is  provided  with  a  steel  bevel  wheel  about  6  feet  diameter 
and  steel  pinion  about  2  feet  9  inches  diameter,  5-inch  pitch, 
14  inches  wide. 

The  positive  screw  motion  for  forcing  the  rolls  together  during 
the  rolling  ensures  an  even  thickness  and  full  section  and  true 
rolling  of  the  tire,  which  is  said  to  be  lacking  in  mills  with  only 
a  hydraulic  forcing  motion.  The  hydraulic  motion  is  found  to  be 
more  or  less  yielding,  and  to  give  unequal  thicknesses  and  hollow 
places  on  the  surface  of  the  tire.  About  100  wagon  tires  can  be 
made  per  day. 

As  far  back  as  1835,  John  Day  invented  and  patented  a  method 
of  making  railway  wheel  centres  which  was  universally  adopted 
and  remained  in  use  until  a  comparatively  recent  period.  He 
welded  up,  in  wrought  iron,  ~|~- shaped  pieces,  each  of  which  formed 
a  portion  of  the  circular  rim,  one  spoke  and  a  part  of  the  hub  or 
boss.  The  whole  was  gradually  welded  up  by  highly  skilled 
wheel-smiths.  The  hub  being  first  completed,  the  ends  of  the 
portions  of  the  felloes — the  heads  of  the  ~|~'s — did  not  abut 
against  each  other,  filling  pieces  called  ''gluts"  being  welded 
between  them.  Very  great  care  was  required  to  secure  sound 
welds  and  a  good  finish,  the  forgings  undergoing  little  dressing- 
up  after  they  left  the  smith's  shop.  The  hubs  were  bored  to  fit 
the  axle,  and  turned  up  to  a  true  circle.  The  tire  was  subsequently 


44  THE  EAILWAY  LOCOMOTIVE 

shrunk  on.  The  wheels  were  forced  on  to  the  axle  by  hydraulic 
pressure  and  put  in  a  tire  lathe,  by  which  they  were  made  truly 
cylindrical.  Very  beautiful  workmanship  distinguished  most  of 
these  wheels.  About  the  year  1860,  M.  Arbel,  a  French  iron- 
master, greatly  simplified  the  whole  process.  The  separate  parts 
were  stamped  out  in  dies  and  then  grouped.  The  whole  was 
raised  to  a  welding  heat.  A  white-hot  cylindrical  plate  of  iron 
was  put  under  and  another  over  the  inner  ends  of  the  spokes, 
and  the  whole  placed  under  an  exceedingly  powerful  hydraulic 
press  and  welded  up  at  one  blow,  so  to  speak.  Large  driving 
wheels  required  two  heats  to  finish  them.  In  1862,  in  London, 
Herr  Krupp,  of  Essen,  exhibited  cast  steel  disc  driving-wheels. 
That  is  to  say,  the  place  of  the  spokes  was  taken  by  a  disc,  not 
flat,  but  slightly  curved  in  and  out  to  give  elasticity.  They  were 
marvellous  castings  for  the  period,  or  indeed  for  any  period. 
What  they  cost,  who  can  tell  ?  It  was  claimed  for  them  that  they 
did  not  raise  as  much  dust  as  spoke  wheels.  They  were  tried  in 
Germany,  but  nothing  came  of  them. 

For  many  years  the  wrought  iron  wheel  has  been  given  up. 
It  was  very  expensive  to  make  and  so  full  of  centres  of  danger  in 
the  numerous  welds  that  it  was  easily  superseded  by  cast  steel 
as  soon  as  the  steel  founders  had  overcome  the  difficulties  which 
attend  the  production  of  all  steel  castings.  These  difficulties  are 
largely  the  result  of  the  very  high  temperature  at  which  steel 
melts.  One  consequence  is  that  the  metal  when  poured  attacks 
the  surface  of  the  mould,  melting  the  sand,  and  so  not  only 
injuring  the  surface  of  the  finished  casting,  but  developing  gases 
which  are  occluded  in  the  steel,  producing  blow  holes  and  honey- 
combing. The  history  of  steel  founding  is  for  many  years  a 
history  of  failure.  By  degrees  troubles  have  been  overcome,  and 
steel  castings  can  now  be  had  with  as  much  certainty  of  sound- 
ness as  those  of  cast  iron.  To  the  late  Mr.  Francis  Webb, 
locomotive  superintendent  of  the  London  and  North  Western 
Kailway,  the  world  is  indebted  for  an  exceedingly  beautiful 
method  of  casting  steel  wheels.  The  moulds  are  mounted 
horizontally  on  whirling  tables,  and  as  the  metal  is  poured  in  at 
the  centre,  the  moulds  revolve,  and  by  centrifugal  effort  the  metal 


WHEELS  45 

is  forced  outward  into  the  minutest  cranny  of  the  mould,  and 
sound  castings  result.  For  locomotives  and  tenders  the  use 
of  cast  steel  centres  is  now  all  but  universal.  Some  very 
ingenious  machinery  has  also  been  introduced  for  cutting  felloes 
and  spokes  to  shape,  or,  more  strictly  speaking,  taking  off  the 
rough  surface  of  the  casting,  and  so  imparting  that  finish  of 
which  British  engineers  are  proud. 

In  all  cases  the  wheels  are  fitted  with  separate  tires.  These 
are  usually  3  inches  thick  in  the  tread,  before  they  wear.  They 
are  put  in  the  lathe  and  turned  up  from  time  to  time  as  they 
wear  until  they  are  reduced  to  about  one  half  their  original 
thickness,  when  they  are  sent  to  the  scrap  heap  and  replaced  by 
new  tires.  The  wheel  centre  never  wears  out,  and  breakages  are 
very  rare.  It  is  a  matter  of  the  last  importance  that  the  tires 
shall  be  firmly  secured  on  the  wheels.  The  shrinking  on  is  a 
very  simple  matter.  The  tire  is  bored  out  a  small  fraction  of  an 
inch  too  small  in  diameter  to  go  on  the  wheel  centre  cold.  The 
usual  allowance  for  shrinkage  is  as  follows :  for  4  feet  internal 
diameter,  '042  inch  ;  for  5  feet,  '049  inch ;  6  feet,  '058  inch, 
which  are  the  thicknesses  of  wires,  Nos.  19, 18,  and  17,  Birmingham 
wire  gauge.  The  centre  is  laid  flat  on  a  large  circular  cast  iron 
slab  similar  to  that  which  may  be  seen  outside  village  smithies, 
and  used  for  putting  tires  on  wooden  cart  wheels.  Close  by  is  a 
reverberatory  furnace,  in  which  tires  are  heated  while  resting  on 
a  sand  bed  to  little  more  than  the  temperature  of  boiling  water. 
A  couple  of  labourers  take  out  a  tire  with  the  aid  of  a  small 
crane,  and  brushing  away  dirt  they  drop  it  down  on  the  wheel 
centre.  If  it  is  a  shade  tight  the  blow  of  a  heavy  wooden  pounder 
sends  it  home.  As  it  cools  it  contracts,  and  seizes  the  wheel 
centre.  In  some  cases  the  tire  is  heated  by  a  ring  of  gas  jets, 
urged  by  a  moderate  blast.  This  is  cleaner  and  much  less  likely 
to  set  up  oxidation  of  the  surfaces  than  in  the  furnace.  For 
some  sections  of  tire,  as  will  be  understood  further  on,  the  process 
is  reversed.  The  tire  is  laid  on  the  plate  and  the  cold  wheel 
centre  is  dropped  into  it.  Much  care  is  taken  that  the  boring 
of  the  tire  and  the  turning  of  the  wheel  centre  shall  be  so 
managed  that  the  tire  shall  not  be  stressed  when  in  place  to 


46 


THE  EAILWAY  LOCOMOTIVE 


much  more  than  about  one-third  of  its  elastic  limit.  The 
difference  in  diameters  is  expressed,  as  stated  above,  in  terms  of 
a  fraction  of  an  inch  per  foot  in  diameter  of  the  wheel.  The 
fraction  varies  with  the  nature  of  the  steel  used,  and  indeed  with 


FIG.  33. — Tire  sections,  Lancashire  and  Yorkshire  Bail  way. 

the  views  of  the  wheel  maker.  Usually  the  amount  of  contrac- 
tion allowed  for  is  the  result  of  practical  experience  rather  than 
of  theoretical  estimation.  It  would  not  be  safe  to  rely  on 
friction  to  hold  a  tire  on,  and  particularly  a  driving-wheel  tire. 
The  most  obvious  way  of  securing  the  wheel  centre  and  the  tire 
is  to  rivet  them  together,  and  this  was  the  method  used  almost 


WHEELS 


47 


universally  for  several  years.  The  holes  in  the  tire  were  made 
larger  outside  than  in,  and  taper  rivets  with  counter-sunk  heads 
were  used  so  that  the  tire  could  be  trued  up  several  times,  the 
tapered  rivet  of  course  retaining  a  good  hold.  But  the  tires 
often  broke  through  the  holes,  riveting  was  given  up  as 
dangerous,  and  numerous  very  ingenious  devices  were  invented 
and  patented  for  securing 
tires  without  boring  holes 
in  them.  Some  of  these 
are  illustrated  in  the 
drawings  of  wheel  sec- 
tions on  pp.  46,  47,  and 
52.  The  illustrations 
given  in  Fig.  33  are 
sections  of  standard 
engine,  carriage,  and 
wagon  tires  on  the  Lanca- 
shire and  Yorkshire  Bail- 
way.  The  thin  flange  is 
used  on  middle  wheels  to 
give  more  clearance  on 
curves  for  reasons  already 
i'ully  explained.  The 
engine  tire  is  secured  by 
about  a  dozen  screwed  set 
bolts  and  an  outer  lip,  the 
object  of  which  is  to  pre- 
vent the  wheel  from  being 
forced  outward  through 
the  tire,  as  in  rounding  curves. 


BetweenTires 


JL i>^X_ 


. 
Between  Rails 


riving  Tires  Fo\  6  Wheels 
Uoupfyd  Goods  arid  Tank 
'Engines. 


FIG.  34.— Standard  tire  and  rail,  Great 
Eastern  Railway. 


The  wagon  tire  is  given  because 
it  illustrates  a  very  popular  method  of  securing  tires.  Here  the 
wheel  centre  is  dropped  into  the  tire,  which  has  an  outer  lip  just 
like  the  engine  tire.  Then  a  ring  A  is  put  in — there  is  sufficient 
clearance  between  it  and  C.  This  is  then  forced  home  by 
the  ring  B,  which  is  of  soft  steel.  One  end  is  put  in  place 
first  and  driven  home.  The  rest  is  then  gradually  forced  into 
place,  and  then  C  is  beaten  down  on  it  all  round  with  swages 


48 


5 


THE  EAILWAY  LOCOMOTIVE 

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WHEELS 


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THE  KAILWAY  LOCOMOTIVE 


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52 


THE   KA1LWAY  LOCOMOTIVE 


I  Locomotive 
~f.  Thick  Flanges 
6.  Thin  Flanges 


and   sledge   hammers.      An   exceedingly  firm   job   is   made   in 
this  way. 

Fig.  34  is  a  section  of  a  standard  Great  Eastern  Kailway  tire. 
A  ring  A  is  dropped  in  here  as  in  the  wagon  tire,  Fig.  33,  but  it 
is  secured  in  its  place  by  counter-sunk  rivets,  B.  When  a  tire  has 

to  be  removed  the  rivet  head  at  one  end 
is  drilled  off,  and  it  can  then  be  driven 
out.  If  the  tire  were  broken  in  half  a 
dozen  places  it  could  not  leave  the  wheel. 
The  thinning  of  the  flange  for  the 
central  pair  of  wheels  in  a  six-coupled 
engine  is  shown  by  the  dotted  lines. 
The  standard  section  of  the  Great 
Eastern  main  line  rail  is  also  given. 
The  slight  inward  "  cant  "  always  used 
in  order  that  the  coned  tire  may  get  a 
fair  bearing  all  over  the  rail  table  is  to 
be  noticed. 

The  difference  between  wheel-tire  sec- 
tions on  various  railways  is  not  very 
great,  and  recently  a  standard  section 
has  been  proposed  by  the  Engineering 
Standard  Committee.  The  accom- 
panying table,  for  which  the  author 
is  indebted  to  Mr.  George  Hughes, 
mechanical  engineer-in-chief  of  the 
Lancashire  and  Yorkshire  Railway, 
explains  itself.  Ifc  will  be  seen  that  it 
includes  not  only  locomotive  tires,  but 
those  of  coal  and  goods  wagons.  The 
figures  which  it  contains  have  never  been 
made  public  before.  They  give  minute  information  as  to  the 
dimensions  adopted  on  thirty-two,  that  is  to  say  all,  the  principal 
railways  in  the  United  Kingdom.  The  three  sections  given  on 
this  page  accompany  the  tables. 

Returning  now  to  the  construction  of  wheels,  it  may  be  said 
that  the  practice  of  securing  tires  by  steel  screwed  pins  passing 


WHEELS  53 

through  the  felloes  and  som  e  way  into  the  tire  has  become  quite 
usual.  It  is  very  simple  and  cheap.  The  screwed  studs  are  a 
tight  fit  and  seldom  or  never  work  loose.  When  a  tire  has  to 
be  renewed  they  are  easily  screwed  out.  The  tire  is  heated  by 
a  ring  of  gas  jets  until  it  is  sufficiently  expanded,  when  it  is  lifted 
off.  It  will  be  enough  to  add  here  that  probably  as  many  as 
fifty  different  practicable  methods  of  securing  tires  on  railway 
wheels  have  been  patented,  if  not  tried,  on  various  railways  at 
home  and  abroad. 


CHAPTEE   VI 


WHEEL    AND    RAIL 

THIRTY  or  forty  years  ago,  while  rails  were  still  made  of 
wrought  iron,  the  weights  of  locomotives  gradually  increased. 
The  load  on  driving  wheels  at  last  reached  as  much  as  nine 
tons  on  each.  The  result  was  that  rails  began  to  give 
way.  They  split  along  the  top,  and  their  ends  "  were  beaten 
into  besoms."  Numerous  devices  were  schemed  to  get  over  the 

difficulty.  We  need  only  now 
concern  ourselves  with  one. 
It  was  agreed  that  if  a  rail- 
way wheel  was  itself  elastic 
the  rail  would  be  spared  much 
hardship.  A  modern  driving 
wheel  weighs  with  the  tire 
complete  from  three-quarters 
of  a  ton  to  one-and-a-quarter 
tons,  according  to  the  dia- 
meter. This  is  dead  weight 
and  not,  like  that  of  the  engine,  spring-carried.  In  the  United 
States  a  Mr.  Griggs  mounted  his  tires  on  hardwood  wedges 
driven  between  the  felloe  and  the  tire,  with  the  immediate 
result  that  he  greatly  prolonged  the  life  of  his  tires.  In  this 
country  Mr.  Bridges  Adams,  the  inventor  of  the  traversing 
axle  box  already  referred  to,  invented  and  patented  about  1858, 
and,  what  is  more  to  the  purpose,  fitted  engines  and  waggons 
with,  the  wheel  shown  in  Fig.  35.  It  is  stated  that  he  got  excel- 
lent results.  A  steel  ring  or  rings  was  interposed  between  the 
tire  and  the  centre.  The  ring  was  supposed  to  give  way  slightly 
under  the  tread  of  the  wheel.  The  system  got  a  fair  trial  on 


FIG.  35. — Adams'  elastic  wheel. 


WHEEL   AND  EAIL  55 

several  lines,  with  the  result  that  the  lives  of  the  iron  tires  then 
used  were  more  than  doubled.  All  devices  of  this  kind  were, 
however,  rendered  unnecessary  by  the  universal  adoption  of 
steel  rails,  which  will  not  split,  and  steel  tires.  It  is  worth 
notice  that  these  last  were  looked  on  with  much  doubt  at  first 
by  locomotive  superintendents,  as  it  was  held  that  a  hard  steel 
tire  could  not  get  a  good  grip  of  a  hard  steel  rail.  There  was 
some  truth  in  the  argument,  but  not  much.  The  mention  of 
it  leads  directly,  however,  to  a  very  important  question  which 
is  best  considered  here,  although  it  has  only  indirectly  to  do 
with  the  locomotive  considered  as  a  vehicle — a  very  expressive 
word  first  applied  by  a  French  engineer,  Count  Pambour, 
namely  "  adhesion." 

It  is  not  necessary  to  do  more  than  call  attention  to  the  fact 
that  a  locomotive  depends  for  its  motion  along  the  rails  on  the 
same  causes  as  those  which  determine  the  movement  of  a 
bicycle  or  a  motor  car.  The  engine  tries  to  turn  the  driving 
wheel  round.  This  it  cannot  do  unless  the  wheel  moves  for- 
ward, because  of  the  friction  between  its  rim  and  the  road.  Now 
if  we  confine  our  attention  to  a  driving  wheel  and  a  rail  we 
shall  find  much  that  repays  consideration.  The  surface  of  the 
tire  is  very  hard — so  hard  that  it  can  scarcely  be  cut  by  a  file, 
and  turning  a  tire  up  is  a  tedious  process,  and  can  only  be 
carried  out  by  special  tools.  The  surface  of  the  rail  although 
softer  is  also  hard.  The  hard  and  rigid  tire  rests  on  a  hard 
and  rigid  rail — what  is  the  contact  surface  between  them  ? 
Absolute  hardness  and  stiffness  would  entail  a  line  contact 
across  the  rail  table,  because  a  geometrical  circle  can  touch  a 
straight  line  or  double  tangent  only  at  a  geometrical  point. 
In  practice,  of  course,  some  give  and  take  occurs,  The  tire 
flattens  and  the  rail  bends  a  little,  and  so  contact  becomes  more 
than  a  line.  As  far  back  as  1845,  Mr.  Samuelson  carried  out 
some  experiments  on  the  Eastern  Counties  Eailway — now  the 
Great  Eastern — to  ascertain  the  area  of  contact.  He  used  gold 
leaf  slips  pushed  under  a  driving-wheel  in  front  and  behind,  and 
measured  the  distance  between  them.  The  weight  on  the  rail 
was,  however,  only  about  three  tons.  In  1865  the  author  made 


56  THE  EAILWAY  LOCOMOTIVE 

some  experiments  on  the  same  railway,  by  Mr.  Sinclair's  per- 
mission, with  the  same  object,  and  with  several  locomotives 
having  driving  wheels  5  feet  to  6  feet  6  inches  in  diameter,  and 
carrying  loads  of  five  to  five-and-a-half  tons  on  steel  tires  in  fair 
order.  A  part  of  the  rail  being  well  cleaned,  the  engine  was 
brought  over  the  spot  and  two  slips  of  thin  stiff  paper,  or  in 
some  cases  thin  sheet  iron  only  -^^  of  an  inch  thick,  were 
placed  on  the  rail,  one  in  advance  and  the  other  in  the  rear  of 
the  vertical  line  descending  from  the  axle  through  the  locus  of 
contact  of  the  wheel  and  the  rail.  These  slips  were  then  brought 
together  as  closely  as  the  wheel  would  permit.  That  is  to  say, 
they  were  wedged  between  the  tire  and  the  rail  until  the  distance 
between  these  was  so  small  that  the  slips  could  go  no  further. 
It  is  obvious  that  so  long  as  the  tire  is  removed  from  the  rail  by 
the  smallest  conceivable  fraction  of  an  inch  no  contact  exists. 
It  is  also  clear  that  the  curve  of  the  tire  near  the  point  of 
contact  and  the  rail  very  nearly  approximate  to  parallel  lines. 
That  is  to  say,  the  curve  of  the  tire  and  the  rail  table  includes 
so  small  an  angle  that  we  are  justified  in  making  a  considerable 
deduction  from  the  length  of  contact  surface  as  determined  by 
these  experiments.  A  mean  of  six  experiments  gave  f  inch. 
The  length  of  surface  of  true  contact  was,  however,  not  more 
than  half  this,  or  say  T3F  inch.  The  breadth  of  surface  of  contact 
measured  by  the  bright  ribbon  worn  on  the  rail  table  would  be 
about  1J  inches,  and  the  whole  area  of  contact  say  a  fraction 
over  one  square  inch.  In  this  case,  however,  the  rail  was  of 
iron,  and  did  not  weigh  more  than  about  68  Ibs.  to  the  yard  ; 
the  rails  of  the  present  day  weigh  from  90  Ibs.  to  105  Ibs.  per 
yard,  and  the  whole  road  is  incomparably  more  rigid  than  any- 
thing existing  in  1865.  There  is  every  reason  to  think  that,  at 
all  events  with  fairly  new  tires  and  new  rails,  the  surface  of 
contact  may  not  exceed  half  a  square  inch.  Now  the  total  load 
on  the  rail,  including  the  weight  of  the  complete  wheel,  with  its 
axle,  axle  box,  and  spring,  will  be  anything  between  eight  and 
nine  tons.  Consequently  the  stress  between  wheel  and  rail  will 
be  at  the  rate  of  at  least  8  by  2,  or  sixteen  tons  per  square  inch, 
and  may  reach  very  much  more,  as  well  as  much  less,  when  the 


WHEEL  AND   KAIL  57 

engine,  running  at  high  speed,  is  also  rolling  on  its  springs. 
There  is  besides  another  and  very  important  factor  exerting  its 
influence  on  the  relations  between  wheel  and  rail  which  will  be 
understood  when  the  internal  disturbing  forces  are  dealt  with. 
How,  it  may  be  asked,  can  a  rail  table  escape  being  crushed  by 
a  load  so  heavy  as  sixteen  tons  to  the  square  inch,  which  is  close 
to  or  above  the  elastic  limit  of  many  rail  steels  ?  The  tire  is  so 
hard  that  it  may  escape.  The  only  explanation  is  that  the 
portion  of  steel  which  carries  the  load  is  supported  by  the  metal 
all  round.  It  is,  so  to  speak,  in  the  same  position  as  would  be 
a  steel  peg  driven  into  a  hole  in  the  rail.  It  cannot  spread  or 
move  in  any  direction,  and  therefore  the  rail  table  is  not  torn  to 
pieces  all  at  once,  but  is  slowly  disintegrated. 

It  has  been  necessary  to  consider  this  point  at  considerable 
length  because  two  factors  of  great  importance  are  involved.  In 
the  first  place,  the  weight  that  may  be  placed  on  any  one  pair 
of  wheels  is  limited  by  two  considerations.  The  first  is  what 
will  the  rails  stand  ?  the  second  is  what  will  the  bridges  stand  ? 
Both  these  are  affected  by  the  performance  of  the  locomotive 
as  a  vehicle. 


CHAPTEK  VII 

ADHESION 

THE  author  has  written  to  little  purpose  if  he  has  not  made  it 
clear  that  the  pressure  of  a  wheel  on  a  rail  continually  varies. 
Now  the  better  the  design  of  the  engine  the  less  will  this  varia- 
tion be.  Thus,  the  use  of  balance  beams  will  assuredly  distribute 
weight,  rendering  the  whole  machine  more  flexible  vertically. 
But  it  may  be  taken  as  proved  that,  in  this  country  at  all  events, 
a  load  of  twenty  tons  must  never  be  exceeded  on  two  wheels,  and 
that  in  good  practice  eighteen  tons  is  considered  the  maximum. 
It  will  be  seen  presently  that  if  the  load  could  be  doubled,  or 
even  increased  by  50  per  cent.,  important  advantages  would  be 
gained.  As  for  bridges  they  could  be  strengthened,  but  it  would 
be  impossible  to  make  tires  or  rails  that  could  endure  the  addi- 
tional stress.  The  rail  tables  would  give  out  for  the  reasons 
stated  above,  and  the  tires,  however  hard,  would  be  very  short- 
lived. 

In  practice  it  is  the  rule  to  put  the  greatest  possible  weight 
on  the  driving  wheels,  because  this  weight  determines  the  effi- 
ciency of  the  locomotive  as  a  hauling  machine.  The  conditions 
prevailing  between  wheel  and  rail  are  quite  outside  those  of 
ordinary  friction,  in  that  the  loads  carried  are  excessive.  It  has 
become  the  custom,  therefore,  to  speak  of  locomotive  "  adhesion," 
the  word  being  used  in  a  sense  quite  different  from  that  given 
to  it  in  dictionaries ;  what  is  its  co-efficient  we  shall  see  further 
on.  It  must  be  kept  steadily  in  mind  that  if  the  phenomena 
of  locomotive  adhesion  had  no  existence  engines  with  smooth 
driving  wheels  would  possess  no  power  of  locomotion.  Adhesion 
is  as  necessary  as  steam  in  the  cylinder  or  coal  in  the  fire-box. 
It  lies  at  the  root  of  every  calculation  and  enters  into  every 


ADHESION  59 

formula  intended  to  determine  the  tractive  power  of  a  locomotive. 
Again,  after  a  certain  point  has  been  reached,  raising  pressures 
or  increasing  the  size  of  cylinders  or  boilers — the  augmentation^ 
in  short,  of  every  element  that  represents  energy — will  not  confer 
the  least  practical  advantage.  On  the  foothold,  so  to  speak,  of 
an  engine  depends  its  hauling  power.  Adhesion  means  foot- 
hold, no  more  and  no  less.  What  its  relations  are  to  ordinary 
friction  has  been  the  subject  of  many  discussions ;  that  it  is 
akin  to  statical  friction  is  clear,  because  the  tire  is  always  at  rest 
however  fast  the  train  is  running  with  regard  to  the  rail,  unless 
the  wheel  slips.  It  would,  however,  be  mere  waste  of  time  to 
try  to  'draw  a  parallel  between  the  two.  Eailway  authorities 
have  long  since  made  up  their  minds  and  settled  on  a  co-efficient 
for  adhesion  which  has  proved  to  be  of  sufficiently  general 
application,  and  so  nearly  accurate  that  the  design  of  any 
locomotive  can  so  far  be  based  on  it  with  satisfactory  results. 
In  this  country  the  co-efficient  is  one-sixth.  This  means  that, 
unless  the  force  tending  to  make  the  wheel  revolve  measured  at 
the  point  of  contact  with  the  rail  is  greater  than  one-sixth  of  the 
vertical  stress  between  wheel  and  rail,  the  wheel  will  not  slip. 
Thus,  if  the  load  is  nine  tons,  then  the  turning  moment  must 
exceed  1'5  tons,  or  the  wheel  will  not  slip.  In  the  United  States 
it  is  usual  to  take  the  co-efficient  at  one-fifth  or  a  little  more. 
Climate  exercises  a  very  important  influence  on  adhesion.  The 
co-efficient  is  highest  when  the  rails  are  quite  clean,  dry,  and 
moderately  warm.  Under  a  tropical  sun  the  co-efficient  is  a 
little  reduced.  When  a  rail  is  thoroughly  wet  and  washed  clean 
the  adhesion  does  not  suffer  much.  In  fog  or  damp  weather, 
particularly  if  the  rail  is  dirty,  as  it  is  sure  to  be  near  cities 
because  of  smoke,  adhesion  almost  vanishes.  The  wheel  spins 
round  on  the  rail  without  moving  the  engine.  Various  devices 
have  been  schemed  for  augmenting  adhesion,  one  of  which — the 
coupling  of  driving  wheels — must  be  considered  here,  because 
the  use  of  coupled  wheels  affects  the  performance  of  the  loco- 
motive as  a  vehicle,  and  modifies  its  design  very  considerably. 

As  we  have  seen,  by  degrees  the  outside  bearing  was  given  up, 
and  in  the  present  day  the  inside  bearing  alone  is  almost  always 


60  THE  EAILWAY  LOCOMOTIVE 

used  in  Great  Britain  for  passenger  engines.  Exceptions  may, 
however,  be  found  in  other  countries.  Statistics  carefully  col- 
lected by  the  late  William  Adams  on  the  North  London  Kailway 
showed  that  steel  crank  axles  with  inside  bearings  would  run 
about  120,000  miles  without  failure,  while  those  with  outside 
bearings  had  a  life  of  only  about  60,000  miles.1  With  the  much 
larger  cylinders  and  heavier  pressures  of  the  present  day  the 
disparity  in  endurance  would  no  doubt  be  much  greater. 

In  pursuit  of  greater  adhesion,  two,  three,  or  more  pairs  of 
wheels  are  coupled  so  that  they  must  all  revolve  together.  The 
coupling  might  be  effected  by  cogged  wheels  or  by  chains,  but  a 
far  more  simple  and  elegant  device  is  used.  In  each  driving 
wheel  a  crank  pin  is  fitted,  and  a  rod  extends  from  crank  pin  to 
crank  pin.  The  pins  at  opposite  sides  of  the  engine  are  set  at 
90  degrees  apart,  so  that  if  all  the  pins  at  one  side  are  in  a 
horizontal  line,  and  so  on  the  dead  centre,  all  those  at  the  other 
side  are  fully  "  alive."  The  result  is  that,  as  we  have  said,  any 
number  of  wheels  may  be  coupled.  The  adhesion  of  the  loco- 
motive is,  therefore,  proportionately  augmented ;  for  let  it  be 
supposed  that  an  engine  has  four  driving  wheels  6  feet  in 
diameter,  each  pressing  on  the  rail  with  a  weight  of  eight  tons — 
no  coupling  rods  are  on — then  the  weight  for  adhesion  is  16  tons, 

and  the  co-efficient  of  adhesion  being  -,  we  have  — =2*66  tons. 

b  b 

If  now  we  put  on  coupling  rods,  we  get  the  adhesion  due  to  the 
second  pair  of  wheels,  which  is  also  2*66  tons,  and  the  total 
adhesion  is  now  5*32  tons,  and  so  on.  It  must  not  be  supposed, 
however,  that  this  advantage  can  be  secured  without  paying  for 
it.  It  is  well  known  that  the  resistance  of  the  locomotive  regarded 
as  a  vehicle — or,  as  it  is  sometimes,  though  not  with  strict 
accuracy,  called,  the  rolling  resistance— is  augmented  by  coupling 
rods.  Various  estimates  of  the  resistance  have  been  made.  The 
late  Patrick  Stirling,  of  the  Great  Northern  Kailway,  often 
asserted  that  coupling  rods  always  meant  an  extra  fuel  consump- 
tion of  something  over  one  pound  of  coal  per  mile,  or  say 
5  per  cent. 
1  These  mileages  do  not  apply  to  modern  practice  with  steel  crank  axles. 


ADHESION  61 

When  two  axles  only  have  to  be  coupled,  the  inequalities  of 
the  road — either  end  of  the  rod  can  rise  or  fall — have  no  effect. 
If  three  are  coupled  it  is  essential  that  a  joint  shall  be  put  in 
the  coupling  rod  to  permit  the  axle  centres  to  rise  and  fall  above 
and  below  this  horizontal  line.  The  trailing  end  of  each  section 
of  the  coupling  rod  is  extended  past  the  crank  pin,  and  an  eye 
is  forged  in  it,  between  the  jaws  of  which  the  leading  end  of  the 
following  section  of  the  coupling  rod  is  secured  by  a  pin  put 
through  the  eye.  This  secures  flexibility  in  a  vertical  plane. 
The  crank  pins  are  got  up  dead  true  by  grinding,  and  the  bear- 
ings are  in  the  present  day  brass  bushes  lined  with  white  metal, 
and  forced  and  pinned  into  eyes  at  each  end  of  the  side  rod. 
Adjustable  coupling  rod  ends  have  long  since  been  given  up  in 
this  country.  When  they  get  too  slack  the  bushes  can  be  driven 
out  and  replaced  by  new  bushes.  The  side  rods  are  invariably 
made  in  the  present  day  each  of  a  single  steel  forging.  Formerly 
they  were  made  in  three  pieces  of  the  best  forged  scrap  iron, 
that  is  to  say,  there  were  the  two  heads,  one  for  each  end,  and  a 
middle  length.  There  were  thus  two  welds  in  each  rod,  and 
breakages  constantly  occurred  at  the  welds.  Then  an  improve- 
ment was  effected  by  making  each  head  in  one  piece  with  half 
the  length  of  the  rod,  and  this  saved  one  weld.  But  this  is  all 
now  ancient  history.  The  stresses  which  a  side  rod  has  to 
withstand  are  severe.  A  very  moderate  knowledge  of  geometry 
will  suffice  to  show  that  every  portion  of  a  side  rod  describes  as 
regards  the  engine  a  circular  path,  and  is  consequently  submitted 
to  centrifugal  effort.  There  are  besides  tensile  and  compression 
stresses.  There  is  as  a  result  some  form  of  rod  which  will  give 
the  maximum  strength  with  the  minimum  of  material.  What 
this  form  is  has  been  ascertained  by  mathematicians.  Their 
investigations  would  be  out  of  place  here ;  but  the  reader  who 
cares  for  further  information  may  be  referred  to  the  Engineer  for 
January  16  and  23,  February  20,  and  March  6,  1903,  where  he 
will  find  the  whole  subject  elaborately  treated  at  great  length  in 
a  series  of  papers  by  Mr.  Parr. 

Some  designers  use  fish-bellied  rods,  but  the  favourite  rod,  at 
all  events  for  fast  work,  is  a  straight  parallel  bar,  with  a  channel 


62  THE   EAILWAY  LOCOMOTIVE 

cut  in  each  side  of  it  in  a  milling  machine,  so  that  it  is  in  cross 
section  a  double-flanged  girder  in  miniature ;  such  rods  are 
very  handsome  and  very  good. 

Although  mathematics  would  be  out  of  place  in  this  book,  it  is 
very  easy  to  convey  an  idea  of  the  amount  of  the  stresses  which 
a  side  rod  has  to  endure.  In  a  four-coupled  engine,  assuming 
that  the  adhesion  is  the  same  for  all  wheels,  then  if,  as  is  very 
usual,  the  distance  from  the  centre  of  the  coupling  rod  pins  from 
the  wheel  centre  is  the  same  as  that  of  the  crank  pm  centre  from 
the  centre  of  the  axle,  then  the  stress  on  the  coupling  rod  will 
be  equal  to  one  half  the  total  effort  of  the  steam  on  the  piston, 
the  other  half  being  intercepted  by  the  driving  wheel  just  in  front. 
An  18-inch  piston  has  an  area  of  254'5  square  inches,  and 
if  the  pressure  is  150  Ibs.,  then  the  total  effort  on  the  piston 
=  38175  Ibs.  or  seventeen  tons;  one  half  of  this  is  8'5  tons.  Now 
the  stresses  are  both  push  and  pull,  push  when  the  crank  pins 
are  below  the  centre,  pull  when  they  are  above  them.  The  latter 
is  easily  dealt  with.  A  bar  in  tension  with  a  sectional  area  of 
3  square  inches  would  be  ample.  But  the  push  or  thrust  is  quite 
another  matter,  for  the  bar  must  be  stiff  enough  to  act  as  a  strut 
and  withstand  the  tendency  to  bending.  But  the  centrifugal  stress 
is  much  more  serious.  Let  us  take  the  case  of  a  four-coupled 
engine  with  6-feet  driving  wheels,  running  at  a  little  over  sixty 
miles  an  hour.  The  crank  length  for  the  coupling  rods  is 
12  inches.  The  circle  described  by  the  coupling  rod  pins  and 
therefore  by  every  portion  of  the  rod  is  2  feet  in  diameter,  or 
one-third  that  of  the  driving  wheel.  Now  the  velocity  of  the 
6-foot  driving  wheel  rim  is  88  feet  per  second,  as  regards  the 
engine,  with  which  fact  alone  we  have  to  do.  The  coupling 
rod  rotates  at  one-third  of  the  speed,  or  say  30  feet  per  second. 
The  centrifugal  effort  per  pound  weight  of  rod  is  by  the  rule 
already  stated  a  fraction  under  28  Ibs.  If  the  rod  weighs  250  Ibs., 
then  the  tendency  to  fly  away  from  the  crank  pins  would  be  a 
little  over  three  tons,  and  twice  in  each  revolution  the  rod  will 
be  in  the  condition  of  a  girder,  say  8  feet  long,  and  carrying  a 
distributed  load  of  three  tons.  This  transverse  stress  tends  of 
course  to  break  the  rod.  It  will  be  readily  understood  that  it  is 


ADHESION  63 

of  all  things  desirable  that  the  rod  should  be  made  as  light  and 
as  stiff  as  may  be. 

It  has  been  stated  above  that  the  addition  of  coupling  rods 
augments  the  resistance  of  the  locomotive  as  a  vehicle.  The 
reason  remains  to  be  explained.  The  side  rod  compels  all  the 
coupled  wheels  to  revolve  at  the  same  speed ;  but  they  would 
not  if  left  free  all  make  the  same  number  of  revolutions  in 
running  from,  say,  Euston  to  Birmingham,  unless  for  one  thing 
their  circumferences  were  identical ;  but  this  they  cannot  be,  for 
two  reasons :  in  the  first  place,  however  accurately  they  have 
been  turned  to  the  same  diameter  to  begin  with,  they  will  wear 
unequally.  But,  in  the  second  place,  it  must  be  remembered 
that  the  tires  are  conical,  not  cylindrical,  and  that  some  of  the 
flanges  are  pressed  against  the  outer  and  some  against  the  inner 
rail  in  rounding  a  curve ;  slipping  must  therefore  take  place,  not 
only  as  between  the  outer  and  inner  wheel,  but  as  between  one 
pair  of  wheels  and  another.  This  slipping  is  due  to  the  coupling 
rods.  But  beyond  all  this,  the  coupling  of  wheels  causes  resist- 
ance in  a  way  not  easily  explained,  perhaps  because  the  modus 
operandi  is  not  very  clearly  understood.  In  the  old  sea-going 
days  when  ships  sailed,  and  pursued  and  were  pursued,  it  was 
well  known  that  to  get  the  maximum  speed  {the  utmost  possible 
flexibility  was  needed  in  the  hull  and  rigging ;  and  we  read  of 
chased  schooners  and  luggers  whose  crews  unwedged  the  masts, 
and  even  sawed  deck  beams  through  to  let  the  hull  "  work." 
Now  in  something  the  same  way,  the  more  flexible  and  less  rigid 
the  locomotive  as  a  vehicle  is,  the  less  will  be  its  resistance. 
Coupling  rods  are  more  or  less  inimical  to  this  flexibility.  They 
deprive  the  wheels  of  their  individuality.  The  go-as-you-please 
element  is  eliminated.  To  realise  what  this  means  it  is  necessary 
to  travel  first  on  the  foot-plate  of  an  engine  with  only  a  single  pair 
of  driving  wheels  and  then  on  that  of  a  six-coupled  engine.  Much 
can  be,  and  is,  done,  of  course,  to  render  coupling  as  unobjection- 
able as  possible,  but  it  is  always  regarded  as  a  necessary  evil — a 
something  to  be  got  rid  of,  if  only  it  were  possible. 

It  has  been  said  above  that  various  expedients  to  get  rid  of 
coupling  rods  have  been  proposed  and  tried.     Two  only  need  be 


64  THE  EAILWAY  LOCOMOTIVE 

mentioned  here.  The  first  consisted  in  putting  sharp  sand  on 
the  rail  in  front  of  the  driving  wheel.  Unless  rails  are  very 
"  greasy  "  this  will  usually  bring  up  the  co-efficient  of  adhesion 
to  at  least  one-seventh,  probably  to  one-fifth.  The  sand  is  some- 
times merely  dropped  on  the  rail  through  a  pipe  in  front  of  the 
driving  wheel.  To  this  plan  there  are  various  objections  ;  one  is 
that  sand  is  wasted.  Instead  of  lying  on  the  rail  where  it  is 
wanted  it  falls  off.  Another  is  that  suddenly,  just  when  wheels 
are  revolving  at  a  high  speed  on  a  very  slippery  rail,  one  will  be 
pulled  up  by  sand  and  the  other  will  not.  The  result  is  a  very 
heavy  stress  on  the  crank  axle,  which  has  not  infrequently  been 
twisted  across.  Again  the  sand  is  apt  to  fall  on  to  the  oiled 
plates  on  which  the  tongues  of  crossing  switches  work,  and  cause 
so  much  friction  that  the  signalman  cannot  move  them.  In  the 
present  day,  therefore,  it  is  usual  to  fit  a  small  steam  jet  at  each 
side  of  the  engine  which  blows  a  fine  jet  of  sand  right  into  the 
place  under  the  wheel  where  it  is  wanted. 

Even  in  the  present  day  there  are  many  single  driving  wheeled 
engines  at  work,  and  they  have  always  given  so  much  satisfac- 
tion, they  are  so  easy  on  the  road,  and  economical  in  fuel,  that 
their  use  has  been  abandoned  with  the  utmost  regret.  It  is  worth 
while  to  digress  here  to  say  a  few  words  about  in  many  respects 
the  most  beautiful  locomotives  ever  built.  These  were  the  single 
driver,  outside  cylinder  engines,  to  which  reference  has  already 
been  made,  designed  by  the  late  Mr.  Patrick  Stirling,  while  he 
was  locomotive  superintendent  of  the  Great  Northern  Kailway. 

This  engine  weighed  only  39  tons,  distributed  as  follows : 

Leading  bogie  wheels      .         ...       7  tons. 
Trailing  ,,  ':.*-.  .         .       8     ,, 

Driving  wheels       .         .         .         .         .  16     ,, 

Trailing      „ 8     „ 


Total     .         .         .         .39  tons. 

As  to  the  performance  of  these  engines,  which  conducted 
express  traffic  for  many  years  between  King's  Cross,  Leeds,  and 
York,  it  will  suffice  to  say  that  trains  of  from  16  to  20  coaches 


ADHESION  65 

represented  normal  loads.  As  many  as  28  coaches  have  been 
taken  and  schedule  time  kept.  These  weighed  10  or  12  tons 
each,  or  say  one-half  the  weight  of  a  modern  coach.  From  King's 
Cross  to  Potter's  Bar,  13  miles,  the  work  is  all  uphill — the 
sharpest  curve  15  chains  radius.  The  tractive  effort  of  the 
engine  would  probably  reach  at  slow  speeds  about  9,000  Ibs. 
The  load  under  the  driving  wheels  would  be  35,840  Ibs.,  so 
that  the  co-efficient  of  adhesion  must  have  reached  about  0*25, 
which  could  only  have  been  got  on  a  dry  road  and  with 
sand.  Many  engineers,  however,  believe  that  the  co-efficient 
is  better  under  a  large  than  it  is  under  a  small  wheel.  Some 
years  ago  Mr.  Ivatt  greatly  improved  these  engines  by  adding 
domes  to  them.  These  permitted  the  water  to  be  carried  at  a 
higher  level  in  the  boiler,  a  matter  of  much  importance  in 
climbing  long  hills,  because  the  feed  can  be  cut  off  and  the  heat 
stored  in  the  water  used  in  the  cylinders.  When  the  hill  was 
surmounted  the  boiler  could,  of  course,  be  filled  up  again 


R.L. 


CHAPTEK  VIII 

PROPULSION 

WE  have  now,  it  is  believed,  considered  all  the  external 
disturbing  forces  of  a  locomotive  engine,  the  principle  of  their 
action  and  of  the  methods  adopted  in  combating  them.  Any 
reader  with  a  mathematical  tarn  of  mind  will  not  fail  to  perceive 
that  all  the  questions  involved  admit  of  mathematical  treatment, 
but  everything  of  the  kind  would  be  out  of  place  in  a  book  such 
as  this  which  is  intended  to  explain  in  general  terms  why  the 
locomotive  engine  is  what  it  is.  Thus  the  reason  why  the  front 
or  leading  end  of  an  engine  is  carried  on  a  four-wheeled  bogie 
instead  of  on  two  wheels  has  been  set  forth,  but  no  attempt  has 
been  made  to  treat  the  questions  raised  as  geometrical  problems 
to  be  solved  algebraically. 

At  the  outset  it  was  stated,  it  will  be  remembered,  that  the 
locomotive  regarded  as  a  vehicle  was  subjected  when  running  to 
two  classes  of  disturbing  forces — the  first  external  to  it,  such  for 
example,  as  the  imperfections  of  the  road  on  which  it  moves ;  the 
second,  internal.  The  first  it  has  in  common  with  all  railway 
carriages,  vans,  wagons,  &c.,  and  indeed  all  vehicles  traversing 
streets  or  highways.  The  internal  disturbing  forces  are  quite 
different  in  character,  of  great  importance,  and  not  so  easily 
dealt  with  as  the  external  forces. 

At  this  point  it  becomes  necessary  to  explain  precisely  how 
a  locomotive  is  propelled — a  matter  concerning  which  entirely 
erroneous  ideas  are  generally  held.  Thus  the  accepted  explana- 
tion is  that  the  driving  wheel  pushing  back  against  the  rail,  the 
crank-axle  bearings  push  forward  continuously  against  the  engine 
frames,  the  amount  of  the  push  rising  and  falling  with  the 
position  of  the  crank  and  the  pressure  on  the  piston,  but  always 


PROPULSION  67 

being  forward  in  the  direction  in  which  the  train  is  moving. 
The  author  believes  that  he  was  the  first,  many  years  ago,  to 
publish  a  statement  of  the  true  facts  in  the  Mechanic's 
Magazine. 

The  author  may  be  permitted  to  quote  here  from  a  paper  on 
"  The  Adhesion  of  Locomotive  Engines,"  which  he  read  before 
the  Society  of  Engineers  in  1865.  The  facts  have  been  in  no 
wise  altered  by  the  lapse  of  time  : — 

"  For  the  purpose  of  illustration,  we  will  assume  the  case  of  a 
locomotive  engine  with  a  single  pair  of  drivers  6  feet  in  diameter  ; 
the  cylinders,  outside,  a  minute  fraction  less  than  16  inches  in 
diameter ;  the  pistons  having  a  stroke  of  2  feet,  and  an  area  of 
precisely  200  square  inches.  For  the  present,  let  it  be  further 
assumed  that  one  cylinder  only  is  in  action,  the  other  being 
uncoupled,  and  the  pressure  throughout  the  stroke  taken  at 
50  Ibs.  per  square  inch  above  the  atmosphere,  back  pressure,  &c. 
Suppose  now  that  this  engine  is  at  rest  on  the  rails  in  such  a 
position  that  the  crank  stands  up  vertically,  the  crank  pin  being 
directly  above  the  centre  of  the  axle,  and  the  piston  approximately 
at  half  stroke.  If  now  we  turn  on  steam  behind  the  piston,  we 
shall  find  that  it  is  urged  forward  with  a  force  equal  to  10,000  Ibs. 
The  crank  pin  will  also  be  urged  in  the  same  direction  with  a 
similar  force,  less  the  small  amount  of  loss  due  to  the  obliquity 
of  the  connecting  rod,  which  loss  we  may  totally  disregard  in 
the  present  investigation.  The  wheel  we  shall  assume  to  have 
so  much  adhesion  that  no  slipping  takes  place ;  we  may  then 
regard  that  spoke  directly  in  the  vertical  line  below  the  crank 
axle  as  constituting  with  the  crank  a  lever  of  the  second  order, 
in  which  the  load  to  be  moved  (the  engine)  is  placed  between  the 
power  (applied  to  the  crank  pin),  and  the  fulcrum  (the  rail) :  the 
axle  journal  will  then  be  thrust  against  the  forward  brass  with  a 
force  greater  than  that  due  to  the  strain  on  the  piston  bv  an 
amount  exactly  equivalent  to  the  proportion  existing  between  the 
distances  intervening  between  the  crank  pin  and  the  rail,  and  the 
axle  centre  and  the  same  point.  The  engine  would,  therefore, 
tend  to  advance  with  a  force  equal  to  13,333*33  Ibs.,  and  were 
there  nothing  to  be  deducted  these  figures  would  represent  the 

F2 


68  THE  EAILWAY  LOCOMOTIVE 

gross  tractive  force  of  the  machine  while  the  crank  remains 
vertical.  But  from  this  total  we  must  subtract  the  retarding 
force  operating  on  the  hinder  lid  of  the  cylinder,  amounting,  of 
course,  to  a  stress  precisely  equal  to  that  on  the  piston,  or 
10,000  Ibs.,  and  we  find  that  the  gross  effective  force  of  traction 
is  reduced  to  3,333  Ibs.,  the  force  at  the  rail,  or  that  to  be  resisted 
by  adhesion  being  precisely  the  same.  The  hauling  power  of 
the  machine,  therefore,  is  only  due  to  the  lever  action  proper  to 
the  wheel  and  crank,  and  so  far  it  is  certain  that  the  advance  of 
the  machine  is  a  consequence  of  the  pressure  of  the  crank  axle 
on  the  forward  brasses." 

"  But  the  crank  is  above  the  axle  only  during  one  half -revolution, 
and  during  the  other  half  the  state  of  affairs  changes  materially. 
Suppose  all  things  arranged  as  before,  the  crank,  however,  being 
directly  below  the  wheel  centre  instead  of  above  it,  steam  being 
admitted  in  front  of  the  piston.  This  last  tends  to  move  back- 
wards in  the  cylinder,  or  in  a  direction  contrary  to  that  in  which 
we  wish  the  engine  to  move.  This  pressure  is  communicated 
directly  to  the  crank  pin,  and  were  the  wheel  free  it  would 
revolve — but  the  wheel  is  not  free.  It  now  acts  the  part  of  a 
lever  of  the  third  order,  the  power  (the  force  on  the  crank)  being 
applied  between  the  load  to  be  moved  (the  engine)  and  the 
fulcrum  (the  rail).  The  crank  shaft  is,  therefore,  thrust,  not 
against  the  forward  brass,  but  against  that  which  is  behind,  with 
a  force  proportional  to  the  distance  intervening  between  it  and 
the  rail  and  the  crank  pin  and  the  rail.  A  little  calculation  will 
show  at  a  glance  that  the  stress  on  the  pin  being  10,000  Ibs.,  the 
retarding  thrust  on  the  axle  brass  will  be  One-third  less,  or 
6,666  Ibs.,  while  the  force  to  be  resisted  by  adhesion  will  still  be 
3,333  Ibs.  Under  these  conditions  the  machine  would  retrograde 
were  it  not  for  the  force  exerted  by  the  pressure  of  the  steam 
reacting  from  the  piston  on  the  forward  lid  of  the  cylinder, 
amounting  to  10,000  Ibs.,  from  which,  deducting  6,667  Ibs.,  we 
have  3,333  Ibs.,  as  before,  for  the  tractive  force  of  the  machine 
at  that  moment." 

"  From  the  foregoing  it  is  clear  that  a  locomotive  is  propelled 
during  the  forward  stroke  by  the  pressure  on  the  axle  brasses  and 


PKOPULSION  69 

retarded  by  that  on  the  hinder  cylinder  lid ;  while  during  the 
back  stroke,  the  propulsion  of  the  machine  is  due  to  the  pressure 
on  the  forward  lid  of  the  cylinder,  the  strain  on  the  axle  brasses 
directly  opposing  its  advance.  So  far  we  have  only  considered 
the  case  of  an  engine  with  a  single  cylinder,  nor  is  it  necessary 
that  we  should  enter  at  any  length  into  the  phenomena  presented 
in  ordinary  practice.  It  will  be  seen  that  the  introduction  of 
the  second  cylinder  and  piston  acting  at  right  angles  to  the  first 
complicates  the  relations  of  the  stresses  to  which  the  machinery 
is  exposed  without  materially  altering  their  character.  Thus  the 
engine  is  alternately  forced  forward  on  its  path  by  a  cylinder  lid 
located  at  one  corner  and  a  shaft  bearing  placed  in  the  mid  length 
of  the  framing.  If  the  thrust  on  the  axle  boxes  were  steadily 
exerted  in  the  direction  in  which  the  engine  proceeds,  crank 
axle,  brasses,  and  guides  would  give  little  trouble  ;  as  it  is  they 
require  constant  attention." 

To  make  what  takes  place  still  clearer,  let  us  imagine  the  crank 
pin  on  the  dead  centre.  At  the  end  of  one  stroke  the  brass  will 
be  thrust  back  when  steam  enters  the  cylinder,  and  the  front 
cylinder  cover  will  be  thrust  forward,  the  two  efforts  being  equal 
and  opposite.  When  the  piston  is  at  the  other  end  of  the  stroke 
the  conditions  and  efforts  will  be  the  same,  but  in  the  reverse  direc- 
tion. All  the  circumstances  are  analogous  to  those  of  rowing. 
The  rower  exerts  forward  effort  on  the  rowlock,  and  a  backward 
effort  against  the  stretcher.  The  propelling  force  is  the  difference 
between  the  stress  on  the  rowlock  and  that  on  the  stretcher. 

Summing  up,  we  find  that  the  crank  axle  brass  is  pushed  and 
pulled  at  every  revolution  backwards  and  forwards.  If  longi- 
tudinal slackness  existed,  the  axle  boxes  would  knock  in  the  horn 
plates,  and  to  prevent  this  a  driving-wheel  axle  box  is  always 
fitted  with  a  wedge  for  taking  up  wear.  See  Fig.  1. 

If  we  trace  out  the  motion  of  the  piston  it  will  be  readily 
perceived  that  in  space  it  is  continuously  moving  faster  and 
slower  than  the  engine.  This  subject  has  been  dwelt  upon 
because  unless  the  relations  between  the  piston,  cylinder  covers, 
driving  wheels,  and  rails  are  fully  understood  much  that  follows 
will  be  incomprehensible. 


70  THE  EAILWAY  LOCOMOTIVE 

Now,  so  far  the  engine  has  been  dealt  with  as  though  there 
was  only  one  cylinder  and  piston ;  but  there  are  two,  and  their 
lines  of  action  are  on  different  vertical  planes,  and  the  motions 
are  not  simultaneous,  but  rhythmical.  The  cranks  are  at  an  angle 
of  90°  with  each  ether.  The  result  is  that  as  the  engine  advances 
along  the  rails  it  is  propelled,  as  has  been  just  stated,  first  by  a 
cylinder  cover  at  one  side,  then  by  an  axle  box  at  the  other  side, 
then  by  two  axle  boxes,  then  by  two  cylinder  covers,  then  by  a 
cylinder  cover  at  the  other  side.  The  tendency  is  to  set  up 
a  sinuous  motion  in  the  engine.  The  magnitude  of  this  lateral 
movement  depends  on  the  distance  of  the  cylinder  from  the 
longitudinal  centre  of  the  frame  ;  and  the  earlier  outside  cylinder 
six- wheeled  single-driver  locomotives  "  wiggled  "  along  the  road 
to  such  an  extent  that  some  of  them  were  termed  "  boxers  "  by 
the  drivers,  and  to  this  day  an  engine  is  said  "to  box"  when 
the  leading  end  beats  backwards  and  forwards.  In  some  engines, 
indeed,  a  peculiar  action  takes  place  when  the  train  is  running 
on  a  straight  piece  of  track.  A.  rhythmical  motion  takes  place, 
and  the  engine  begins  to  "wander,"  swaying  slowly  from  side  to 
side  across  the  road  in  a  very  alarming  fashion.  The  moment  a 
curve  is  reached  wandering  ceases,  and  it  can  always  be  stopped 
by  shutting  the  regulator  for  a  moment  and  so  throwing  the 
engine  "  out  of  step." 

We  have  then,  in  the  position  of  the  cylinders  and  the  mode  of 
action  of  the  piston  and  crank,  one  internal  source  of  disturbance. 

We  have  so  far  neglected  the  effect  of  the  angular  action  of 
the  connecting  rods.  The  engine  tends  to  revolve  round  the 
crank  axle  with  precisely  the  same  energy  as  the  crank  axle 
tends  to  revolve  under  the  boiler.  When  the  engine  is  running 
forward  the  cross  head  is  pressed  against  the  upper  guide  bar, 
and  tends  to  lift  the  leading  end  of  the  engine  by  an  amount 
which  varies  from  nothing  at  the  end  of  the  stroke  to  a  maximum 
when  the  piston  has  made  a  certain  advance ;  what  this  point 
will  be  depends  on  the  pressure  in  the  cylinder.  Let  the  length 
of  the  connecting  rod  be  7  feet,  and  that  of  the  crank  one  foot, 
then  by  the  composition  and  resolution  of  forces  it  can  be  shown 
that  at  a  point  near  the  middle  of  the  stroke  one-seventh  of  the 


PEOPULSION  71 

whole  pressure  on  the  piston  will  be  exerted  in  lifting  or  attempting 
to  lift  the  leading  end  of  the  engine.  An  equal  effort  will  tend  to 
force  the  crank  down  on  the  rail ;  thus,  let  the  piston  be  18  inches 
in  diameter  and  24  inches  in  stroke,  and  the  connecting  rod 
7  feet  long,  if  the  net  pressure  in  the  cylinder  at  a  point  a  little 
in  advance  of  half  stroke  is  50  Ibs.  on  the  square  inch,  the  thrust 

or  pull  of  the  piston  rod  will  be  about  9  tons,  and  the  upward  effort 

9 
on  the  slide  bars  will  be  —  =  1*287  tons  nearly,  but  the  lifting 

effort  varies  in  amount  continuously,  and  so  we  have  introduced 
what  many  writers  regard  as  a  distinct  factor  of  disturbance.  It 
is  worth  while  to  consider  whether  it  is  or  is  not,  because  there 
is  a  principle  involved.  Let  us  take  the  case  of  an  engine  carried 
on  six  wheels,  without  a  bogie.  The  load  on  each  leading  wheel 
is  six  tons,  the  weight  of  each  wheel  is,  say,  half  a  ton,  including 
its  spring,  axle  box,  and  half  the  axle;  the  total  load  is  then 
13  tons  under  the  leading  wheels. 

Now  it  will  be  seen  that  any  lifting  effort  exerted  above  the 
axle  box  can  be  resisted  only  by,  in  this  case,  six  tons,  the  wheel, 
axle  boxes,  axle  and  springs,  regarded  as  so  much  dead  weight, 
remaining  unaffected.  There  is  then  at  each  side  of  the  engine 
six  tons  holding  down  the  guide  bar.  The  upward  lift  on  the 
guide  bar  exerted  by  the  cross  head  represents  only,  as  we  have 
seen,  less  than  1J  of  a  ton,  and  would  have  no  effect  whatever  as 
a  disturbing  force  were  it  not  for  the  fact  that  the  external 
disturbing  forces  come  into  play  and  prepare  the  way,  so  to 
speak,  for  this  particular  factor.  We  have  already  referred  to 
the  "  rolling  "  of  an  engine.  Experiments  made  some  years  ago 
in  France  have  shown  that  an  engine  may  roll  so  much  that  the 
whole  of  the  load  is  taken  off  the  leading  springs  and  axle  box  at 
one  side  first  and  then  the  other,  and  the  wheels  kept  the  track 
only  because  of  their  own  weight.  It  appears  again  that  when 
an  engine  is  running  round  a  curve  the  centrifugal  effort  may 
take  a  very  large  percentage  of  weight  off  the  inside  wheel.  In 
that  case,  again,  the  slide- bar  thrust  might  be  very  much  felt, 
tending  to  exaggerate  rolling,  and  so  promoting  unsteadiness. 
When  a  bogie  is  used  the  conditions  are  somewhat  different — 


72  THE  EAILWAY  LOCOMOTIVE 

rolling  has  little  or  no  effect  on  the  bogie- wheel  loads.  Indeed, 
one  of  the  advantages  of  the  bogie  is  that  it  is  exempt  from  the 
influence  of  internal  disturbing  forces  up  to  a  certain  point, 
which  will  be  considered  presently.  On  the  whole,  then,  although 
it  is  right  to  include  cross-head  thrust  as  an  internal  disturbing 
factor,  care  must  be  taken  not  to  exaggerate  an  importance 
which  is  under  any  circumstances  small.1 

1  On  the  London  and  South  Western  Hallway  certain  locomotives  were 
many  years  ago  built  by  Mr.  Beattie.  They  were  six- wheeled  four- coupled 
outside  cylinder  engines;  all  the  wheels  had  inside  bearings.  They  rolled  so 
much  that  outside  bearings  were  put  on  the  leading  axles,  and  the  springs 
were  fitted  under  the  lower  guide  bars,  as  there  was  nowhere  else  to  put 
them.  The  expedient  was  quite  successful. 


CHAPTER   IX 

COUNTER-BALANCING 

WE  have  now  to  consider  a  much  more  important  source  of 
disturbance  than  any  named  yet. 

When  a  body  of  any  shape  revolves,  it  tends  to  turn  round  its 
centre  of  gravity.  Rankine  has  put  this  fact  so  admirably  that 
the  author  cannot  do  better  than  quote  from  the  treatise  "  On  the 
Steam  Engine  and  other  Prime  Movers, "page  27,  second  edition, 
1861 :  "  The  whole  centrifugal  force  of  a  body  of  any  figure,  or 
of  a  system  of  connected  bodies,  rotating  about  an  axis  is  the 
same  in  amount  and  direction  as  if  the  whole  mass  were  con- 
centrated at  the  centre  of  gravity  of  the  system.  When  the  axis 
of  rotation  traverses  the  centre  of  gravity  of  the  body  or  system, 
the  amount  of  the  centrifugal  force  is  nothing,  that  is  to  say, 
the  rotating  body  does  not  tend  to  pull  its  axis  as  a  whole  out  of 
place.  The  centrifugal  forces  exerted  by  the  various  rotating 
pieces  of  a  machine  against  the  bearings  of  their  axles  are  to  be 
taken  into  account  in  determining  the  lateral  pressures  which 
cause  friction,  and  the  strength  of  the  axles  and  framework.  As 
these  centrifugal  forces  cause  increased  friction  and  stress,  and 
sometimes  also  by  reason  of  their  continual  change  of  direc- 
tions produce  detrimental  or  dangerous  vibration,  it  is  desirable 
to  reduce  them  to  the  smallest  possible  amount ;  and  for  that 
purpose,  unless  there  is  some  special  reason  to  the  contrary,  the 
axis  of  rotation  of  every  piece  which  rotates  rapidly  ought  to 
traverse  the  centre  of  gravity,  that  the  resultant  centrifugal  force 
may  be  nothing.  It  is  not,  however,  sufficient  to  annul  the 
effect  of  centrifugal  force  that  there  should  be  no  tendency  to 
shift  the  axis  as  a  whole ;  there  should  also  be  no  tendency  to 
turn  it  into  a  new  angular  position.  To  show,  by  the  simplest 


74  THE  RAILWAY  LOCOMOTIVE 

possible  example,  that  the  latter  tendency  may  exist  without 
the  former,  let  the  axis  of  rotation  of  the  system,  shown  in 
Fig.  36,  be  the  centre  line  of  an  axle  revolving  in  brasses  at 
E  and  F.  At  B  and  D  let  two  arms  project  perpendicularly 
to  that  axle  in  opposite  directions  in  the  same  plane,  carrying 
at  their  extremities  two  heavy  bodies  H  and  C.  Let  the  weight 
of  the  arms  be  insensible  as  compared  with  the  weights  of 
those  bodies  ;  and  let  the  weight  of  the  bodies  be  inversely  as 
their  distances  from  the  axis;  that  is,  let  H  HE  =  C  CD,  let 
H  C  be  a  straight  line  joining  the  centres  of  gravity  of  H  and  C 
and  cutting  the  axis  in  G ;  then  G  is  the  common  centre  of 
gravity  of  H  and  C,  and  being  in  the  axis  the  resulting  centri- 
fugal force  is  nothing.  In  other  words,  let  a  be  the  angular 
velocity  of  the  rotation,  then  the  centrifugal  force  exerted 

O  TT        TT  TD 

on  the  axis  by  H  =  -  -  ;    the  centrifugal  force  exerted 

u 

c?  C    (TT) 

on  the  axis  by  C  =  -  — ,  and  these  forces  are  equal  in 

magnitude  and  opposite  in  direction,  so  that  there  is  no  ten- 
dency to  remove  the  point  G  in  any  direction.  There  is, 
however,  a  tendency  to  turn  the  axis  about  the  point  G,  being 
the  product  of  the  common  magnitude  of  the  couple  of  centri- 
fugal forces  above  stated  into  their  leverage ;  that  is  the 
perpendicular  distance  B  D,  between  their  lines  of  action.  That 
product  is  called  the  '  moment  of  the  centrifugal  couple ' ;  and 
is  represented  by  Q  .  B  D,  Q  being  the  common  magnitude  of  the 
equal  and  opposite  centrifugal  forces.  That  couple  causes  a 
couple  of  equal  and  opposite  pressures  of  the  journals  of  the  axle 
against  their  bearings  at  E  and  F,  in  the  directions  represented 
by  the  arrows ;  and  of  the  magnitude  given  by  the  formula 

BD 

Q  .  .     These  pressures  continually  change  their  directions 

E  F 

as  the  bodies  A  and  C  revolve  ;  and  they  are  resisted  by  the 
strength  and  rigidity  of  the  bearings  and  frame.  It  is  desirable 
when  practicable  to  reduce  them  to  nothing,  and  for  that 
purpose  the  points  B,  G  and  D  should  coincide,  in  which  case 


COUNTEE-BALANCINa  75 

the  centre  line  of  the  axle  E  F  is  said  to  be  a  permanent 
axis." 

The  meaning  of  this  passage  should  be  fully  mastered  by  the 
student ;  what  follows  is  based  on  it. 

In  the  locomotive  engine  we  have  a  crank  axle,  and  it  is  quite 
clear  that  that  axle  is  out  of  balance ;  or  if  we  take  a  pair  of 
driving  wheels  mounted  on  a  straight  axle,  these  alone  will  be 
out  of  balance  because  of  the  crank  pins. 

Let  us  picture  to  ourselves  a  crank  shaft  caused  to  revolve  in 
a  lathe  between  the  centres,  and  it  will  be  seen  at  once  that  the 
conditions  resemble  those  laid  down  by  Kankine,  and  that  not 
only  will  the  axle  tend  to  revolve  round  a  centre  of  gravity,  but 
about  two  centres,  one  proper 
to  each  crank;  the  conse- 
quence  is  that  a  peculiar 
"  wobbling  "  motion  would 
take  place  unless  the  bearings 
held  it  steady,  and  that  then 
the  bearings  would  have 
thrusts  and  pulls  to  withstand 
which  would  vary  in  magni-  FlG-  36.— Centrifugal  couples, 

tude  as  the  square  of  the  number  of  revolutions  made  per  minute. 
At  first  sight  it  seems  to  be  enough  to  balance  the  crank,  say  by 
back-weights,  as  is  done  in  marine  engines,  and  indeed  in  some 
locomotives,  but  this  will  not  suffice.  The  forces  to  be  balanced 
are  much  greater  than  that  due  to  the  weight  of  the  crank. 

We  have  the  piston  rod  and  cross  head  moving  in  a  straight 
line,  and  the  connecting  rod,  each  portion  of  which  describes  a 
path  varying  from  a  straight  line  to  a  circle,  according  to  its 
position  in  the  length  of  the  rod.  Now  the  piston  rod,  &c., 
have  momentum  and  inertia.  It  is  not  necessary  to  go  here 
into  the  mathematics  of  the  problem  in  detail.1  It  is  enough 
to  say  that  Mr.  Arthur  Rigg,  in  his  treatise  on  the  steam  engine, 

1  Those  readers  who  may  wish  to  see  the  problem  treated  mathematically 
cannot  do  better  than  consult  a  paper,  "  The  Counter  Balancing  of  Locomotive 
Engines,"  by  Edmund  Lewis  Hill,  read  and  discussed  at  a  meeting  of  students 
of  the  Institution  of  Civil  Engineers,  January  30,  1891. 


76  THE   EAILWAY  LOCOMOTIVE 

showed,  it  is  believed  for  the  first  time,  that  the  influence  of  the 
reciprocating  masses  of  a  steam  engine  may  all  be  dealt  with  as 
though  the  weights  were  concentrated  at  the  centre  of  the  crank 
pin.  Their  effect  is  to  cause  the  crank  axle  to  try  to  revolve  round 
a  centre  which  is  not  identical  with  its  mechanical  centre ;  and 
taking  four  positions  only  for  illustration,  to  make  the  crank 
axle  bearing  push  forward,  accelerating  the  engine  ;  push  back- 
ward, retarding  the  engine ;  push  downward,  augmenting  the 
apparent  weight  on  the  rail ;  and  push  upward,  reducing  the 
load  on  the  rail. 

It  must  be  steadily  kept  in  mind  that  we  have  two  disturbing 
forces  to  deal  with,  first  the  weight  of  the  crank  cheeks,  pins, 
and  eccentrics.  This  can  be  dealt  with  by  putting  balance 
weights  on  the  wheel  bosses  or  inside  the  rims ;  and  inasmuch 
as  these  weights  would  be  symmetrically  outside  the  cranks,  and 
the  cranks  would  be  symmetrically  inside  them,  the  common 
centre  of  gravity  would  fall  about  the  middle  of  the  length  of 
the  crank  axle,  and  there  would  be  no  centrifugal  couple  pro- 
duced, and  the  axle  would  revolve  harmoniously  in  its  bearings. 
Balancing  of  this  kind  is  very  old.  Among  the  first  engines 
built  by  Bury,  Curtis  and  Kennedy,  the  wheels  were  made  of 
cast  iron  with  wrought  iron  tubular  spokes  ;  the  bosses  had 
balance  weights  cast  on  them.  The  second  disturbing  force  is 
the  momentum  and  inertia  of  the  piston,  cross  head,  piston 
rod,  and  connecting  rod.  The  effect  of  these  factors  on  any 
high-speed  engine  is  well  known.  Their  effect  on  a  locomotive 
is  usually  made  the  subject  of  rather  abstruse  mathematical 
investigation.  For  instance,  Makinson,  on  "  The  Internal  Dis- 
turbing Forces  in  a  Locomotive,"  a  paper  which  was  read 
before  the  Institution  of  Civil  Engineers,  which  will  be  found  in 
voL  ccii.  of  the  Transactions,  page  106,  may  be  cited,  or  Mr. 
Hill's  paper,  already  quoted.  Happily  the  whole  problem 
admits  of  being  stated  in  general  terms  with  quite  sufficient 
accuracy  for  ordinary  purposes.  Although  the  parts  move  in 
straight  lines  and  ovals  they  can  be  treated,  as  has  just  been 
said,  as  if  they  revolved  round  the  centre  of  the  crank  axle ; 
thus  in  the  accompanying  diagram,  Fig.  37,  we  have  a  crank 


COUNTEK-BALANCING 


77 


axle  A,  a  crank  B,  and  a  crank  pin  C.  Now  the  effort  of  a 
piston,  connecting  rod,  &c.,  may  be  regarded  as  the  same  as 
that  which  would  be  produced  if  a  symmetrical  ring  D,  equal  to 
the  reciprocating  portions  in  mass,  that  is  to  say,  in  weight, 
surrounded  the  crank  pin.  This  simplifies  the  matter  enor- 
mously. Thus,  let  us  suppose  that  the  total  weight  of  the 
reciprocating  parts  is  500  Ibs.,  that  the  engine  has  6-feet  driving 
wheels,  and  runs  at  sixty  miles  an  hour.  Then  the  speed  of  the 
crank  which  is  one  foot  long,  as  regards  the  engine  is  29*3  feet 
per  second,  and  by  the  rules  already  give.n  the  centrifugal 
effort  or  "  force,"  as  Kankine  calls  it, 
will  be,  in  round  numbers,  nearly  six 
tons.  When  the  crank  is  horizon- 
tally forward  the  axle  is  forced 
against  the  axle  box,  urging  the 
engine  onward ;  and  when  the  crank 
is  horizontally  pointing  backwards, 
then  the  engine  is  retarded  by  a 
similar  amount.  To  understand  what 
really  takes  place,  let  us  consider  the 
piston  at  the  termination  of  the 
forward  stroke.  It  has  to  be  made 
to  move  backward  at  once  with  a 
velocity  accelerated  from  nothing  to 

about  1,000  feet  per  minute,  and  the  crank  has  to  drag  the  piston 
away  from  the  end  of  the  cylinder.  In  the  same  way,  when 
acceleration  ceases  about  mid-stroke,  the  piston,  &c.,  pushes  on 
the  crank  which  has  to  retard  it  and  bring  it  to  rest.  The  amount 
of  push  and  pull  will  be  modified  by  the  pressure  of  the  steam 
in  the  cylinder  in  a  way  sufficiently  obvious. 

It  will  be  seen  now  that  after  all  allowances  have  been  made 
we  have  very  serious  disturbing  forces  to  deal  with.  The  general 
result  of  the  combination  is  to  make  the  engine  move  by  jumps 
instead  of  going  steadily  forward,  and  inasmuch  as  the  influence 
of  want  of  balance  is  not  symmetrical,  because  the  cranks  are  not 
opposite  each  other,  but  at  angles  of  90  degrees,  the  whole  effect 
on  the  engine  is  to  set  up  a  violent  fore  and  aft  oscillating 


78  THE  KAILWAY  LOCOMOTIVE 

movement,  which  is  not  only  objectionable  and  even  dangerous,  but 
inimical  to  speed.  Although  much  was  done  in  a  rule  of  thumb 
way  before  D.  K.  Clark  took  the  subject  up,  it  may  be  safely  said 
that  he  was  the  first  to  introduce  the  systematic  use  of  balance 
weights  in  the  driving  wheels  of  locomotives,  and  this  he  did 
after  many  experiments,  putting,  in  1856,  balance  weights  into 
the  driving  wheels  of  the  Canute  on  the  London  and  South 
Western  Eailway.  The  engine  had  already  had  the  dead  weights 
balanced  by  85  Ibs.  bolted  inside  the  rims  of  the  driving  wheels. 
Mr.  Glark  added  186  Ibs.  for  each  wheel.  "  The  engine  runs  so 
much  more  steadily  and  freely  with  the  new  balance  weights  as 
to  take  the  engine  men  by  surprise.  On  the  first,  day  after  the 
alteration,  the  stations  were  considerably  overshot  by  the  engine, 
although  steam  was  shut  off  and  the  brakes  applied  at  the  usual 
distance  from  the  stations.  The  saving  in  fuel  by  the  improving 
of  the  counterweights  of  the  engine  was  estimated  at  20  per 
cent." 

It  must  be  kept  carefully  in  mind  that  balance  weights 1  are 
used  for  two  purposes — in  the  first  place,  to  deal  with  dead 
weights ;  in  the  second  place,  to  deal  with  the  forces  due  to  the 
reciprocation  of  the  moving  parts.  Now  it  so  happens  that  the 
useful  action  of  these  latter  compensating  weights  is  limited  to  a 
portion  of  each  revolution,  while  centrifugal  force  is  constant  all 
through  each  revolution.  The  consequence  is  that  the  weights 
put  in  to  deal  with  reciprocating  masses  are  superfluous  for  large 
portions  of  each  revolution,  and  they  are  not  only  superfluous, 
but  mischievous.  What  we  want  in  any  case  is  not  their 
centrifugal  energy,  but  their  momentum,  which  is  quite  a 
different  thing. 

Thus  their  centrifugal  effort  when  they  are  at  the  top  of  the 
wheel  tends  to  lift  the  wheel  off  the  rail,  and  again  when  it  is  at 

1  The  words  "balance  weights"  are  misleading.  We  have  the  small 
weights  necessary  to  balance  the  rotating  masses,  and  properly  so  called ; 
but  the  remaining  and  much  larger  weights  are  not  intended  to  "  balance  " 
anything ;  they  are  really  compensating  weights  intended  to  neutralise  the 
effect  of  momentum  and  inertia  in  the  reciprocating  masses  on  the  rest  of 
the  engine  ;  thus  when  a  piston  is  flying  backward  the  compensating  weight 
is  flying  forwards. 


COUNTER-BALANCING  79 

the  bottom  it  tends  to  force  the  wheel  down  on  the  rail :  the 
result  of  the  first  is  to  tend  to  cause  slipping ;  the  result  of  the 
second  is  what  is  known  as  "hammer  blow,"  very  destructive 
to  the  rail.  To  reduce  the  mischief  as  much  as  possible  in 
practice  the  custom  is  to  balance  all  revolving  weights  and  only 
three- fourths  of  the  reciprocating  weights  with  inside  cylinder 
engines.  With  outside  cylinder  engines  the  balancing  is  a  little 
more  complete,  the  moving  parts  being  generally  lighter.  The 
result  is  that  the  inertia  and  momentum  of  the  reciprocating 
parts  are  not  quite  compensated,  but,  on  the  other  hand,  the 
mischief  done  by  centrifugal  effort  is  reduced  ;  and  indeed  com- 
plete compensation  is  not  necessary,  because  compression  at  the 
beginning  of  each  stroke  tends  to  bring  the  piston  quietly  to 
rest,  and  lead — that  is,  the  admission  of  steam  before  the  crank 
reaches  the  dead  point — helps  the  piston  away  from  the  end  of 
the  cylinder.  While  on  the  whole  compensation  is  quite  satis- 
factory, it  must  not  be  forgotten  that  it  is  bought  at  a  price  ; 
centrifugal  force  comes  in  as  a  factor  which  would  be  gladly 
spared,  and  has  indeed  been  eliminated  in  a  way  which  will  be 
explained  further  on. 

The  balance  weights  usually  take  the  form  of  the  new  moon. 
The  reason  why  will  be  explained  when  the  locomotive  as  a 
steam  engine  is  considered. 

In  former  practice  the  cast  iron  balance  weights  were  placed 
between  the  spokes  just  under  the  rim  and  secured  by  two  flat 
wrought  iron  segmental  plates  riveted  through  the  cast  iron, 
one  outside,  the  other  inside.  In  modern  engines  they  form  part 
of  the  steel  wheel  centre,  being  cast  with  it.  Sometimes  they 
are  hollow  and  lead  is  poured  into  them  so  that  precisely  the 
proper  weight  can  be  provided.  For  reasons  which  cannot  be 
explained  here,  in  some  cases  the  centre  of  gravity  of  the  weight 
is  not  diametrically  opposite  to  the  cranks ;  in  others  it  is 
divided.  Thus  the  cranks  are  balanced  by  "  back  weights  "  as 
in  marine  engines,  which  are  in  effect  prolongations  of  the  crank 
cheek  backwards.  Again,  the  coupling  rods  have  to  be  taken 
into  account.  Obviously  they  balance  some  of  the  weight. 
But  their  presence  introduces  further  complications.  Several 


80  THE   RAILWAY  LOCOMOTIVE 

designers  divide  the  balance  and  compensating  weights  among 
all  the  driving  wheels,  contending  that  in  this  way  hammer 
blow  is  minimised.  But  generally  only  the  weight  of  half  the 
side  rod  and  the  crank  pin  is  balanced  in  a  coupled  wheel. 

Although  compensation  and  balance  weights  are  always  pro- 
vided, and  rightly  so,  as  if  they  described  circular  paths,  it  must 
be  remembered  that  they  only  do  this  as  regards  the  engine. 
Their  true  path  in  space  is  a  cycloid,  and  this  as  regards  the 
rail  has,  it  is  held  by  some  engineers,  an  effect  on  the  relations 
between  wheel  and  rail.  Thus  they  point  out  that  the  effect  of 
hammer  blow  does  not  take  place  immediately  under  the  balance 
weight,  but  before  it  has  reached  the  rail.  Experiments  show 
that  the  place  of  what  may  be  termed  impact  varies  with  the 
speed  and  other  conditions,  so  that  it  is  by  no  means  easy  to  say 
what  is  really  the  best  angle  with  the  cranks  at  which  to  fix  the 
weights.  Mathematical  investigations  have  not  given  results 
which  necessarily  coincide  with  those  obtained  in  practice. 
There  is  in  consequence  no  such  thing  as  absolute  uniformity ; 
and  balancing  and  compensating  are  carried  out  very  much  in 
the  way  that  experience  has  shown  to  give  the  smoothest  running 
engine  without  much  regard  to  theory. 

In  the  United  States  the  effect  of  hammer  blow  has 
received  far  more  consideration  than  in  this  country.  Kails  are 
not  made  with  the  same  care  as  in  Great  Britain,  and  a  sharp 
controversy  has  gone  on  between  the  locomotive  superintendents 
and  the  rail  makers,  the  latter  asserting  that  it  is  hammer 
blow  that  splits  and  breaks  the  rails. 

In  order  to  supply  some  information  on  the  subject  a  number 
of  experiments  were  carried  out  on  the  testing  plant  of  the 
Pennsylvania  Kailway  at  the  St.  Louis  Exhibition.  It  will  be 
remembered  perhaps  that  this  testing  plant  consisted  essentially 
of  a  set  of  wheels,  the  distances  between  which  could  be 
adjusted,  and  fitted  with  very  powerful  dynamometer  brakes.  The 
engine  to  be  tested  was  run  into  the  shed,  and  its  wheels  were 
supported  on  the  brake  wheels  which  revolved  when  the  driving 
wheels  turned.  The  locomotive  was  prevented  from  running  off 
the  brake  wheels  by  its  draw  bar,  which  was  secured  to  a 


COUNTER-BALANCING 


81 


tractometer,  the  other  end  of  which  was  secured  to  a  strong 
anchorage.  This  plant  was  in  the  main  a  reproduction  of  that 
designed  by  Professor  Goss  for  the  Purdue  University.  A  very 
similar  plant  has  now  been  in  use  for  nearly  two  years  at  the 
Great  Western  Eailway  Works,  Swindon. 

In  order  to  settle  what  the  effect  of  the  balance  weights  might 
be,  Professor  Goss,  by  whom  the  experiments  were  carried  out, 
adopted  the  ingenious  expedient  illustrated  in  the  accompanying 


ELEVATION. 
FIG.  38. — Wire  test  for  hammer  blow. 

engraving,  Fig.  38.  Annealed  steel  wires  '06  inch  in  diameter 
were  passed  between  the  driving  and  the  brake  wheels,  and 
subsequently  measured  with  a  micrometer  calliper  at  intervals  of 
5  inches.  Guide  pipes  f  inch  in  diameter  were  used  to  lead  the 
wires  to  the  point  of  contact  between  the  wheels.  Before  being 
used  the  wires  were  carefully  straightened,  cut  to  lengths  3  feet 
greater  than  the  circumference  of  the  driving  wheel,  and  rubbed 
bright  with  emery  cloth.  Behind  the  points  of  contact  of  the 
driving  and  supporting  wheels  were  galvanised  iron  cones  placed 
R.L.  G 


82  THE   EAILWAY  LOCOMOTIVE 

to  throw  the  wires  away  from  the  machinery  after  passing  the 
wheels.  A  small  groove  was  cut  across  the  driving-wheel  tire  in 
the  same  plane  and  on  the  same  side  of  the  wheel  as  the  outside 
crank  pin.  This  gave  a  reference  mark  on  the  wires  so  that  the 
wheel  positions  could  be  determined.  It  would  be  impossible  to 
go  into  a  consideration  of  the  results  obtained  at  any  length.  The 
conclusions  of  the  most  interest  reached  by  Professor  Goss  are  that 
wheels  balanced  according  to  the  usual  rules,  which  require  all 
revolving  parts,  and  from  40  to  80  per  cent,  of  all  reciprocating 
parts,  to  be  balanced — this  latter  portion  being  equally  dis- 
tributed among  the  wheels  coupled — are  not  likely  to  jump  the 
track  through  the  influence  of  the  weight.  Where  a  wheel  is 
lifted  through  the  action  of  its  balance  weight  its  rise  is  com- 
paratively slow  and  its  descent  rapid.  The  maximum  lift  occurs 
after  the  counterbalance  has  passed  its  highest  point.  The 
rocking  of  the  engine  on  its  springs  may  assist  or  oppose  the 
action  of  the  counterbalance  in  lifting  the  wheel.  It  therefore 
constitutes  a  serious  obstacle  in  the  way  of  any  study  of  the 
precise  movements  of  the  wheel.  The  contact  of  the  moving 
wheel  with  the  rail  is  not  continuous  even  for  those  portions  of 
the  revolution  where  the  pressure  is  greatest,  but  is  a  rapid 
succession  of  impacts.  There  is  reason,  however,  to  believe 
that  the  lifting  does  not  affect  the  wheel  as  a  whole,  but  is  the 
result  of  vibration,  which  in  its  turn  is  a  consequence  of  the 
elasticity  of  the  metals  concerned,  namely,  the  surface  of  the 
tire  and  the  rail. 

These  experiments  go  to  show  that  the  received  theory  that  a 
driving  wheel  rolls  quietly  on  a  rail  with  an  insistent  pressure 
varying  rhythmically  throughout  each  revolution  is  not  quite 
consistent  with  the  facts,  the  phenomena  of  the  relations  of 
wheel  and  rail  being  complex  instead  of  simple. 

The  reader  has,  it  is  believed,  been  now  placed  in  possession  of 
the  principal  facts  concerning  the  locomotive  as  a  vehicle.  He 
has  seen  something  of  the  forces  to  which  it  is  subjected,  and 
of  the  methods  adopted  in  dealing  with  them.  But  it  must 
be  carefully  kept  in  mind,  particularly  by  the  student,  that 
the  mathematical  inwardness  of  the  subject  remains  for  his 


COUNTEK-BALANCING-  83 

consideration,  and  that  even  the  observed  facts  have  not  been 
completely  set  forth.  Thus,  for  example,  the  influence  of  elasticity 
in  the  roads  on  the  locomotive  has  not  been  considered,  and  yet 
elasticity  is  a  thing  that  has  to  be  carefully  provided  in  permanent 
way.  For  reasons  already  stated,  and  indeed  restated,  a  com- 
plete consideration  of  the  locomotive  as  a  vehicle  would  be  out  of 
place  in  this  volume. 


SECTION   II 

THE  LOCOMOTIVE   AS  A  STEAM  GENERATOR. 
CHAPTER   X 

THE    BOILER 

IT  is  probable  that  as  many  as  fifty  different  types  of  loco- 
motives are  at  work  to-day  on  the  railways  of  the  world.  If 
we  except  a  small  number  of  motor  railway  coaches,  which 
have  vertical  boilers,  all  have  boilers  presenting  the  same 
general  features.  We  have  at  one  end  a  box  with  a  round 
or  flat  top,  at  the  other  end  another  box  with  a  chimney  set 
on  top  of  it,  and  the  two  boxes  are  connected  by  a  cylindrical 
barrel.  It  will  be  seen  at  once  that  the  form  and  arrangement 
lend  themselves  admirably  to  being  carried  on  wheels.  We 
have  only  to  look  at  a  locomotive  and  try  to  adapt  a  vertical 
or  rectangular  boiler  to  the  engine  framing  and  wheels  to 
arrive  at  the  obvious  conclusion  that  it  is  not  possible  to  improve 
on  the  general  design.  In  fact,  the  external  characteristics 
of  the  locomotive  may  be  said  to  have  been  fixed  for  us  by 
conditions  which  cannot  be  altered ;  and  that  is  the  reason  why, 
notwithstanding  the  many  attempts  which  have  been  made  to 
modify  the  external  characteristics  of  the  locomotive,  they  remain 
in  the  main  what  they  were  to  begin  with. 

As  this  book  is  not  historical,  it  will  be  enough  to  say  that 
from  the  day  when  George  Stephenson  ran  the  Rocket  at  the 
Rainhill  competition  on  October  6,  1829,  to  this  moment,  the 
locomotive  boiler  has  remained  unaltered  in  principle,  and  this 
notwithstanding  the  fact  that  various  modifications  have  been 


THE   BOILEE 


85 


proposed  and  tried.     The  locomotive  engine  boiler  will  therefore 
be  dealt  with  as  it  is  and  not  as  it  might  be. 

We  have,  as  has  been  said  above,  at  one  end  a  rectangular 
box  with  a  flat  or  circular  top.  Inside  the  box  is  placed  another 
made  of  copper,  or  of  steel  plates,  with  a  space  between  the  two 
boxes  which  is  rilled  with  water.  The  first,  or  external  fire-box, 
is  riveted  to  a  cylindrical  "  shell  "  or  "  barrel."  To  the  other 
end  of  the  shell  is  secured  the  smoke-box ;  the  internal  fire- 
box is  united  to  the  smoke-box  by  a  great  number  of  tubes 
about  2  inches  in  diameter.  The  boiler  is  filled  with  water 
to  such  a  height  as  will  drown  the  fire-box  and  the  tubes.  A 


FIG.  39. — Sectional  diagram  of  boiler. 

grate  is  fixed  in  the  bottom  of  the  fire-box,  and  a  fire  being 
lighted  on  it,  the  smoke  and  gas  pass  from  the  fire  through 
the  small  tubes  and  into  the  smoke-box,  and  thence  up  the 
chimney.  The  heat  is  communicated  to  the  water  through  the 
walls  and  roof  of  the  fire-box,  and  the  metal  of  the  tubes.  What 
is  left  goes  to  waste  up  the  chimney.  The  accompanying 
diagram,  Fig.  39,  shows  a  locomotive  boiler  in  section.  Here  A 
is  the  internal  fire-box.  B  B  are  two  of  the  flue  tubes  and  C  the 
smoke-box,  D  the  chimney,  E  a  door  giving  access  to  C.  A 
brick  arch  is  shown  at  F  and  a  deflector  at  G  to  beat  down 
the  air  entering  through  the  fire  door  on  to  the  burning  coal. 
H  is  the  grate,  I  the  foundation  ring,  K  bridge  stays,  sometimes 
reinforced  by  sling  stays  P  P,  L  is  the  fire  door,  M  screwed  stays. 


86  THE  EAILWAY  LOCOMOTIVE 

Before  considering  in  detail  the  construction  of  a  boiler,  it 
will  be  necessary  to  say  something  of  what  goes  on  inside  it, 
because  it  is  this  that  settles  the  interior  characteristics  of  the 
boiler,  just  as  the  fact  that  a  locomotive  engine  is  a  comparatively 
long  narrow  vehicle  has  settled  its  external  appearance. 

The  first  thing  to  be  done  is  to  burn  coal ;  the  second  to  absorb 
the  heat  given  off  during  the  process,  and  use  it  to  make  steam. 
What  is  subsequently  done  with  the  steam  will  be  discussed  when 
we  come  to  deal  with  the  locomotive  as  a  steam  engine.  It  has 
been  dealt  with  as  a  vehicle.  It  is  now  to  be  dealt  with  as  a 
means  of  turning  water  into  steam. 

It  is  a  curious  truth  that  in  this  extremely  scientific  age  next  to 
nothing  is  known  concerning  the  conversion  of  any  liquid  into  a 
vapour  or  gas.  The  whole  literature  of  the  subject  is  represented 
by  two  or  three  pages  of  Ganot's  "  Physics."  The  question  is 
much  too  large  to  handle  adequately  here,  but  it  cannot  well  be 
passed  over  when  we  bear  in  mind  that  the  durability  of  a  boiler, 
its  safety  from  explosion,  and  the  good  and  bad  qualities  of  the 
steam,  are  all  matters  of  the  utmost  importance,  presenting 
problems  which  depend  for  their  solution  on  a  knowledge  of  how 
steam  is  made  to  the  best  advantage  and  what  it  really  is. 

The  received  theory  is  that  steam  while  in  the  saturated  state, 
that  is,  with  no  free  heat,  is  nothing  more  than  water  with  its 
molecules  driven  asunder  by  heat.  When  steam  is  superheated, 
it  becomes  a  gas  like  air,  that  is  all.  As  an  apt  expression  of  the 
received  concept  of  the  formation  of  vapours — steam  and  gas- 
nothing  can  be  better  than  the  following  extract  from  an  article 
by  Mons.  L.  Houllevigue  in  the  Revue  de  Paris,  of  April  1, 
1903,  translated  by  Chief  Engineer  B.  F.  Isherwood,  United 
States  Navy,  for  the  Journal  of  the  Franklin  Institute. 

"  Physicists  saw  matter  formed  of  molecules  or  aggregated 
molecules  isolated  from  each  other  and  pursuing  each  other  in 
incessant  movement  like  the  particles  of  dust  vibrating  in  the 
sunbeam,  and  from  this  eddying  mass  they  saw  escaping  waves, 
that  propagated  themselves  in  space  by  means  of  an  infinitely 
rare  medium,  which  was  to  the  lightest  of  known  bodies,  hydrogen, 
what  the  density  of  hydrogen  was  to  the  density  of  the  heaviest 


THE   BOILER  87 

metals.  Gases,  especially,  appeared  as  microscopic  projectiles 
darting  in  every  direction  and  continually  bombarding,  without 
loss  of  force,  the  sides  of  the  vessel  that  contained  them,  only  to 
rebound  again  and  recommence  their  eternal  movement.  The 
heat  contained  in  the  gases  took  from  similar  impacts  a  more 
precise  significance ;  it  showed  the  present  energy  of  all  these 
moving  corpuscles.  If  the  gas  be  cooled,  the  velocity  of  the  pro- 
jectiles diminishes,  their  trajectories  flatten,  then  all  the  corpuscles 
collapse,  but  still  retain  eddying  movements  ;  this  is  liquefaction. 
Then,  in  measure  as  more  and  more  energy  is  taken  out  of  them, 
the  vibrating  molecules  make  less  and  less  extended  movements, 
and  the  liquid  contracts  in  cooling.  Very  soon  the  increasing 
nearness  of  the  molecules  to  each  other  enables  them  to  make 
among  themselves  new  interactions,  their  relative  positions 
become  nearly  invariable,  and  the  liquid  solidifies;  but  the 
resulting  solid  is  still  animated  with  life-like  shiverings ;  it  could 
still  be  cooled  down  to  the  point  at  which  its  molecules  would 
repose,  inert,  one  upon  the  other  ;  and  then  the  matter  would 
be  dead," 

Here  we  have  the  whole  process  of  the  conversion  of,  say,  ice 
into  superheated  steam  stated  in  inverse  order. 

Man  produces  more  steam  than  any  other  manufactured  article. 
It  is  quite  impossible  to  ascertain  with  certainty  what  weight  of 
coal  is  burned  annually  in  making  steam  for  the  factories,  mines, 
railways  and  ships  of  Great  Britain.  There  is,  however,  reason 
to  believe  that  not  short  of  60,000,000  of  tons.  Allowing  that 
each  ton  of  coal  will  make  seven  tons  of  steam,  we  have  then  an 
annual  output  of  no  less  than  420,000,000  of  tons  of  steam  for 
this  country  alone,  or  forty-two  times  the  weight  of  iron  we 
make.  All  this  is  manufactured  by  the  aid  of  costly  apparatus, 
and  with  a  certain  amount  of  risk  of  life,  limb  and  property. 

Allowing  35  cubic  feet  to  the  ton,  the  water  converted  into 
steam,  as  stated  above,  would  amount  to  14,700,000,000  cubic  feet, 
which  would  fill  a  lake  100  feet  deep  and  over  2J  miles  long 
and  2  miles  wide.  The  quantities  are  stupendous,  yet,  as  has  just 
been  said,  next  to  nothing  is  known  of  the  nature  of  the  material, 
steam.  The  author  is  quite  prepared  to  find  this  statement 


88  THE  EAILWAY  LOCOMOTIVE 

treated  with  incredulity.  It  will  be  said  that  everything  is 
known,  that  the  literature  of  the  subject  is  profound  and 
practically  complete.  These  statements,  however,  it  will  be 
found  on  examination,  apply  not  to  steam,  but  to  the  apparatus 
by  which  it  is  made,  namely,  boilers  and  furnaces  ;  and  to  that  by 
which  it  is  used,  namely,  engines.  If  nothing  had  ever  been 
written  about  iron  but  treatises  on  the  blast  furnace,  the  con- 
verter, the  mill  and  the  cupola,  no  one  would  say  that  the 
literature  of  iron  and  steel  was  complete.  Let  us  draw  an 
analogy  between  the  blast  furnace  and  the  steam  boiler.  Into 
the  first  we  put  coke  and  ore  and  limestone  and  air,  and  out  of  it 
we  get  pig-iron  and  gas.  Every  step  of  the  process  by  which  the 
iron  and  gas  are  obtained  has  been  made  the  subject  of  careful 
inquiry.  Into  a  boiler  we  put  water  and  we  take  out  steam. 
But  of  the  inwardness  of  the  process  practically  nothing  is  known. 
Things  are  taken  for  granted,  and  when  phenomena  present 
themselves  out  of  the  common  we  are  told  either  that  they  have 
no  real  existence,  that  they  are  quite  usual,  or  that  it  is  not  worth 
while  to  pursue  an  inquiry.  A  great  deal  has  been  written  about 
the  conductivity  of  boiler  plates,  to  name  one  thing,  but  no  one 
cares  to  inquire  how  or  why  the  heat  is  passed  into  the  water,  or 
what  it  does  when  it  gets  in. 

The  accepted  explanation  advanced  by  scientific  men  has  been 
given  above.  Somewhat  different  views  have  recently  been 
advanced  by  physicists  in  the  first  flight  of  scientific  research ; 
but  these  do  not  admit  of  being  briefly  stated,  and  their  extended 
consideration  would  be  out  of  place  in  this  book. 

Descending  from  the  more  or  less  transcendental  region  of  pure 
thermodynamics  to  practice,  let  us  consider  how  the  heat  gene- 
rated by  the  combustion  of  fuel  and  imparted  to  the  water  is 
distributed.  In  other  words,  to  crystallise  our  ideas  the  facts 
must  be  stated  quantitatively.  This  has  never  been  done  in  more 
detail  or  more  lucidly  than  by  Benjamin  Isherwood  in  his 
splendid  "  Kesearches  in  Steam  Engineering."  For  convenience 
of  reference  his  table  has  been  reproduced  on  the  next  page.  It 
will  be  seen  that  he  has  used  the  old  thermal  unit  772  instead  of 
the  modern  unit  774,  but  the  difference  is  of  no  importance,  and 


THE   BOILEE 


89 


some  uncertainty  even  now  exists  as  to  the  precise  foot-pound 
value  of  the  beat  required  to  raise  one  pound  of  water  1°  F. 
Incidentally  it  may  be  pointed  out  that  minute  and  precise  as 
Isherwood's  statement  is,  it  gives  no  clue,  and  pretends  to  give  no 
clue,  to  the  way  in  which  water  is  converted  into  steam.  At  first 


H                              D 

Distribution  of  heat  in  the  conversion  of 
1  Ib.  of  water  at  32°  F.  into  steam  at 
212°  F. 

Thermal 
units. 

Dynamical 
Equivalents. 

Per  cent,  of 
total  Heat. 

D  4-  772. 

H  x  772. 

Total  heat  of  steam  of  212°  from 

water  at  32° 

1,146-600 

885,175-200 

100-000 

fin  creasing  the  temperature   of 

jj 

the  water    from    32°  to  212° 

"3L 

and    lessening   the    cohesion 

\f 

of    the    water    between    32° 

.9  ' 

-4-3 

and  212° 

180-898 

139,653,359 

15-776 

cS 
<D 

m 

Increasing  the  volume  of  water 

w 

L     between  32°  X  212° 

0-0018 

1-4406 

0-0002 

r  Destroying  the  cohesion  of  the 

g 

water  (i.e.,  converting  it  into 

1 

steam  from  the  boiling  point) 

893,666 

689,910,025 

77-940 

(B 

.9- 

Increasing   the   volume  of  the 

-4-3 

water  from  that  which  it  had 

hn 

as  water  at  212°  to  that  which 

PH 

it  had  as  steam  at  212° 

72-0341 

55,610,374 

6-2820 

1,146-600 

885,175-200 

100-000 

sight  it  may  appear  that  if  we  really  understood  all  about  it,  the 
fact  would  have  no  practical  value,  but  this  is  not  the  case. 
There  are  peculiarities  in  the  performance  of  different  locomotives 
which  await  explanation.  There  are  explosions,  such  as  that  at 
St.  Lazare,  in  Paris,1  that  remain  wrapped  in  mystery ;  and  it 

1  On  the  4th  of  July,  1904,  at  11  a.m.,  the  boiler  of  engine  No.  626,  at  the 
time  standing  in  a  cutting  outside  St.  Lazare  Terminus  of  the  Western 
Railway  of  France,  exploded  with  extraordinary  violence.  It  was  literally 


90  THE   EAILWAY  LOCOMOTIVE 

seems  to  be  by  no  means  impossible  that  if  we  possessed  more 
knowledge,  improvements  of  real  value  might  be  introduced  in 
our  methods  of  making  steam.  As  the  reader  proceeds,  it  is 
hoped  that  the  relation  between  what  has  just  been  read  and  the 
facts  of  the  everyday  life  of  the  locomotive  engine  may  become 
more  apparent  than  they  are  for  the  moment. 

blown  to  bits,  the  fragments,  some  of  them  very  small,  being  projected  to 
great  distances,  falling  in  the  neighbouring  streets.  No  one  was  killed, 
though  a  few  people  were  hurt  by  falling  glass  and  flying  gravel.  The 
damage  to  property  was  estimated  at  £80,000.  At  first  it  was  believed  that 
Anarchists  had  put  a  bomb  in  the  fire-box,  as  there  was  no  one  on  the  foot- 
plate at  the  time.  The  theory  was  untenable,  and  three  special  independent 
inquiries  were  carried  out.  Each  reached  a  different  conclusion.  To  this 
day  the  explosion  remains  unexplained.  The  interested  reader  will  do  well 
to  consult  the  "Bulletin  dela  Societe  d' Encouragement "  for  July  31st,  1905, 
where  he  will  find  complete  details  and  illustrations. 


CHAPTEK  XI 


ik «<   c 


A\\ 


THE    CONSTRUCTION    OF    THE    BOILER 

WE  may  now  proceed  to  consider  in  detail  the  construction  of 
the  locomotive  boiler.  No  better  boilers  are  made  than  those 
produced  in  Great  Britain  and  Ireland.  The  railway  companies 
take  care  that  the  material  and  workmanship  of  the  boilers 
made  in  their  own  shops  shall  be  the  best  possible  ;  and  the 
splendid  reputation  possessed  by  our  loco- 
motive engine  building  firms  all  over  the  world 
is  sufficient  testimony  as  to  what  they  can  do. 

We  have  to  do,  in  the  first  place,  with  the 
stresses  to  which  a  boiler  is  exposed.  The 
simplest  case  is  that  presented  by  the  barrel 
or  cylindrical  shell.  In  calculating  the  stress, 
the  curved  area  of  the  plates  is  to  be  treated 
as  though  it  was  flat,  as  shown  in  the  accom- 
panying diagram,  Fig.  40,  wherein  the  dotted 
line  shows  the  shell  as  it  is  and  the  two  full  lines  the  areas 
giving  the  stress.  Let  us  suppose  that  the  shell  is  48  inches  in 
diameter  and  that  it  is  divided  up  into  rings  each  one  inch  long. 
Then  the  area  we  require  is  48  square  inches,  and  the  effort  of 
the  pressure,  100  Ibs.  per  square  inch,  tending  to  separate  the 
halves  of  the  boiler,  is  4,800  Ibs.  on  each  inch  of  its  length. 
Now  the  effort  may  be  supposed  to  be  concentrated  at  the  point  C 
in  each  section,  and  is,  of  course,  resisted  by  two  thicknesses  of 
the  shell,  one  above,  D,  the  other  below,  E.  Let  the  plates  be 
half  an  inch  thick ;  then  the  sectional  area  to  carry  the  pressure 
will  be  one  inch,  and  the  stress  per  square  inch  of  section  of  the 
shell  plates  will  be  4,800  Ibs.,  or  a  little  over  two  tons.  The  total 
bursting  stress  in  a  large  modern  boiler,  with  a  barrel  14  feet 


FIG.  40.— Eadial 

stress. 


92  THE  BAIL  WAY   LOCOMOTIVE 

long  and  5  feet  in  diameter,  carrying  220  Ibs.,  is  in  round  numbers 
900  tons.  If  the  plates  are  half-inch  thick,  then  the  stress  will 
be  13,200  Ibs.,  or  approximately  6  tons  per  square  inch  of 
sectional  area. 

The  facts  have  been  stated  in  this  elementary  way,  because 
many  persons,  students  especially,  find  some  difficulty  in  under- 
standing how  radial  pressures  act,  and  are  disposed  to  think  that 
the  whole  surface  should  be  taken  into  consideration.1 

The  formula  for  calculating  bursting  pressures  are.,  of  course, 
very  simple.  They  will  be  found  in  most  treatises  on  steam 
boilers  and  various  text-books. 

Let  d  =  the  diameter  of  the  boiler  in  inches  ;  t  =  the  thick- 
ness of  the  plate  in  inches  ;  s  =  the  ultimate  strength  of  the 
metal  in  tons  per  square  inch  ;  and  p  the  pressure  in  pounds  per 
square  inch. 

Then  d  p  is  the  total  pressure  on  a  1-inch  length  of  both  sides 
together  ;  2  t  is  the  sectional  area  of  both  sides  ;  and  2  t  s  x 
2,240  =  dp. 

„,,  4,480  ts  dp  d 

Thenp  =       ^;e== 


It  must  not  be  forgotten,  however,  that  a  boiler  shell  is  not 
made  up  of  solid  plates,  but  of  rings  riveted  together,  and  as  no 
riveted  joint,  no  matter  how  made,  can  be  as  strong  as  the 
solid  plate,  a  deduction  must  be  made.  That  is  to  say,  the 
tensile  strength  of  the  solid  plate  must  be  multiplied  by  the 
fraction  co-efficient  proper  to  the  system  of  riveting  employed. 
Thus,  the  joint  may  be  single  or  double  riveted,  or  it  may  have 
a  single  butt  strap,  or  two  butt  straps,  one  inside,  the  other  out. 
In  the  diagram,  Fig.  39,  at  0  a  single  butt  strap  is  shown. 
In  a  general  way  it  may  be  taken  that  the  strength  of  a  single 
riveted  joint  is  56  per  cent,  of  that  of  the  solid  plate,  while  a 
double  riveted  joint  has  a  co-efficient  of  about  78  per  cent.  ;  but 
there  are  various  qualifications  depending  on  the  way  in  which 

1  Some  years  ago  an  inventor,  reasoning  in  this  way,  took  out  a  patent  for 
a  corrugated  piston,  the  expanded  surface  of  which  would  be  much  greater 
than  that  of  a  plane  piston.  The  advantage  to  be  gained  he  explained  with 
some  care. 


THE   CONSTRUCTION   OF   THE   BOILER  93 

the  rivet  holes  are  made.  The  Board  of  Trade  rules  for  marine 
boilers  go  most  elaborately  into  the  question.  The  following 
formulae  are  quoted  from  the  rules  as  laid  down  in  Trail's  "Hand- 
book for  the  Guidance  of  Engineers,  Surveyors  and  Draughtsmen," 
written  in  1888.  Certain  modifications  have  been  made  since, 
which,  however,  do  not  affect  the  formulae.  If  the  plates  and  the 
rivets  and  the  workmanship  comply  with  the  stipulations  laid 
down,  then  the  percentage  of  strength  of  any  joint  or  other  par- 
ticulars of  the  joint  may  be  found  by  the  following  formula  :— 

p  =  pitch  of  rivets  in  inches. 

d  —  diameter  of  rivets  in  inches. 

A  =  area  of  one  rivet  in  square  inches. 

n  •=.  number  of  rivets  in  one  piston  (greatest  pitch). 

°/0  =.  percentage  of  plate  left  between  rivets  of  greatest  pitch. 

°/0  =  percentage  of  rivet  section  as  compared  with  solid 
plate. 

°/0  =  percentage  of  combined  plate  and  rivet  section  when 
the  number  of  rivets  in  the  second  row  is  twice  that 
in  the  outer  row. 

c  =  1  for  lap  or  single  butt-strap  joint. 

c1  =  1-75  for  double  butt-  strap  joint. 

T  =  Thickness  of  plate  in  inches. 
Then  to  find  the  percentage  strength  of  any  given  joint  :— 


100  X  23  X  A  X  re  X  c  _    0/ 

28  X  p  X  T 

Fortunately  the  Board  of  Trade  has  nothing  to  do  with  locomo- 
tive boilers.  If  they  were  made  in  conformity  with  the  formula 
given  above  they  would  be  very  much  heavier  than  they 
are.  A  very  large  factor  of  safety  is  provided  mainly  because  of 
the  corrosion  which  takes  place  at  sea,  and  not  on  land.  The 
locomotive  boiler  again  does  not  work  for  weeks  at  a  time  without 
examination.  The  boiler  is  under  constant  supervision,  and  the 
most  watchful  care  is  exerted  to  secure  immunity  from  explosion. 
The  result  is  that  scantling  can  be  reduced  without  risk  in  a  way 
that  would  not  be  admissible  at  sea.  But  the  Board  of  Trade 


94  THE   RAILWAY  LOCOMOTIVE 

rules  have  been  given  here  because  they  are  of  general  value  as 
guides  to  those  engaged  in  the  designs  of  any  boilers,  locomotive, 
marine  or  stationary,  which  have  riveted  joints. 

The  boiler  barrel  is  made  up  of  two  or  three  rings  according  to 
its  length.  The  plates  are  cut  to  the  proper  length,  and  their 
edges  are  planed.  They  are  then  bent  between  three  rolls  until 
the  ends  of  each  plate  meet,  and  they  are  secured  together  by 
two  butt  straps,  one  inside,  the  other  out,  double  riveted.  In 
some  cases  the  rings  are  secured  end  to  end  by  narrow  hoops 
and  a  double  row  of  rivets  for  each  hoop.  The  whole  inside  of  the 
barrel  is  then  flush  from  end  to  end.  In  other  cases  the  rings 
are  telescopic  ;  that  is  to  say,  each  is  pushed  about  3  inches  into 
the  one  behind  it,  the  largest  ring  being  next  the  fire-box. 
This  is  a  good  plan,  because  it  increases  the  water  space  next  the 
fire-box.  There  are  two  or  three  methods  of  securing  the  barrel 
to  the  fire-box,  but  a  minute  description  of  these  would  be  out  of 
place  here. 

So  far  no  one  has  yet  had  the  courage  to  risk  welding 
longitudinal  seams.  Flues  for  stationary  and  marine  boilers  are 
now  almost  always  welded.  But  the  stress  being  external  tends 
not  to  open,  but  to  close  their  seams.  The  circumferential  seams 
are  exposed  to  precisely  one  half  the  stress,  the  longitudinal 
strength  of  a  tube  with  closed  ends  being  to  the  circumferential 
strength  as  two  to  one.  To  make  this  quite  clear,  let  us  suppose  a 
tube  8  inches  in  diameter,  the  sectional  area  of  which  is  50  square 
inches ;  the  pressure  inside  is  100  Ibs.  on  the  square  inch.  Then 
we  have  100  x  50  =  5,000  Ibs.  tending  to  pull  the  tube  asunder 
endways.  The  circumference  of  the  tube  is  (omitting  fractions) 
25  inches.  The  thickness  of  the  plate  is  0*5  inches.  Then  the 

25 
sectional  area  of  metal  resisting  the  stress  is  -^  =  12*5  square 

inches.  The  bursting  stress  for  length  =  1  inch  =  800  Ibs.,  and 
the  area  of  metal  to  sustain  it  is  one  inch.  But  the  longitudinal 

effort  is  5,000  arid  -  ^7^  =  400,  or  just  one  half  the  bursting 
IZ'o 

stress. 

We  come  next  to  the  flat  surfaces  of  the  inside  and  outside 


THE   CONSTKUCTION  OF  THE  BOILEE  95 

fire-boxes,  and  the  staying  of  these  constitutes  the  most  important 
structural  problem  that  has  to  be  solved  by  the  locomotive  super- 
intendent. No  part  of  the  complete  machine  gives  so  much 
trouble  or  causes  so  much  anxiety  as  the  boiler,  and  it  is  not  too 
much  to  say  that  90  per  cent,  of  this  is  due  to  the  fire-box.  The 
nature  of  these  troubles  will  be  considered  in  some  detail  before 
any  attempt  is  made  to  explain  the  special  means  taken  to  elude 
or  otherwise  get  over  them.  Take,  for  instance,  an  internal  fire- 
box which  is  6  feet  long,  5  feet  deep,  and  3*25  feet  wide.  The 
area  of  the  flat  crown  of  this  box  is,  in  inches,  72  by  39  =  2,80s.1 
Let  the  pressure  be  200  Ibs.,  then  2,808  by  200  —  561,600  Ibs.,  or 
250  tons.  Each  side  has  an  area  of  72  by  60  =  4,320  square 
inches  and  4,320  by  200  =  864,000  Ibs.,  or  more  than  385  tons. 
How  many  persons  realise  as  they  stand  beside  a  locomotive 
that  stresses  so  enormous  represent  the  effort  of  the  steam  to 
escape  ?  900  tons  to  rip  the  shell  open  ;  385  tons  to  force  out  the 
flat  side  of  the  fire  box  ;  250  tons  to  drive  the  fire-box  down  on  the 
rails,  and  blow  the  rest  of  the  boiler  through  the  station  roof. 
Is  it  wonderful  that  the  boiler  of  a  locomotive  should  claim  and 
get  from  day  to  day  more  attention  than  any  other  part  of  the 
machine  ? 

We  have  now  to  consider  how  these  enormous  stresses  are 
carried.  In  the  barrel  they  only  put  the  metal  in  tension,  and 
being  quite  simple  they  can  be  dealt  with  easily  enough.  It 
suffices  to  provide  a  sufficient  section  of  metal  and  adequate 
riveting.  It  is  far  different  with  the  flat  surfaces.  There  is  so 
far  as  the  vertical  portions  of  the  fire-box  are  concerned,  only 
one  method  of  support  available,  namely,  tieing  the  plates  to 
each  other  by  stay  bolts,  and  tieing  the  front  plate  of  the  fire- 
box to  the  plate  at  the  leading  or  smoke-box  end  of  the  barrel. 
There  are  two  methods  in  use  for  supporting  the  top  or  crown 
of  the  fire-box  :  first,  screwed  stays  attach  it  to  the  top  of 
the  outside  fire-box ;  secondly,  girders  are  placed  on  the  top  of 
the  inside  box,  to  which  it  is  secured  by  screwed  bolts.  Both 
these  systems  are  illustrated. 

1  This  is  virtual  area,  being  that  of  the  rectangle  formed  by  the  foundation 
ring.  The  top  of  the  fire-box  is  almost  always  wider  than  this. 


96  THE  EATLWAY  LOCOMOTIVE 

Numerous  experiments  have  been  made  to  ascertain  the  pres- 
sures that  flat  plates  of  iron,  steel  and  copper  will  sustain  when 
supported  by  screwed  stays.  The  results,  however,  of  practice- 
in  other  words,  those  obtained  in  the  regular  performance  of  their 
work  by  locomotives — have  resulted  in  the  almost  universal 
spacing  of  stay  bolts  4  inches  apart,  centre  to  centre,  the 
bolts  being  f  inch  diameter.  Now  these  bolts  are  an  endless 
source  of  trouble,  expense  and  even  danger.  They  are  short, 
the  distance  between  the  two  plates  stayed  varying  from 
2J  inches  as  a  minimum  to  4  inches  as  a  maximum.  The  inside 
fire-box  being  of  copper,  which  has  a  co-efficient  of  expansion  of 
•1722,  while  the  outer  box  is  of  steel  with  a  co-efficient  of  '1145, 
and  the  inner  box  being  besides  always  hotter  than  the  outer 
when  the  fire  is  alight,  it  follows  that  the  inside  box  rises  inside 
the  outer  box,  it  may  be  by  as  much  as  0'25  inch.  This 
cannot  take  place  without  bending  the  stay  bolts,  or  the  plates 
in  which  they  are  set ;  and  inasmuch  as  this  tendency  does  not 
take  place  once  for  all,  but  goes  on  continuously  as  the  tempera- 
ture of  the  furnace  varies,  in  time  the  stays  become  "  fatigued  " 
and  break.  The  only  ways  of  ascertaining  whether  they  are 
broken  or  not  is  by  sounding  the  heads  with  a  hammer — by  no 
means  a  certain  test — or  by  finding  a  bulge  in  the  plate.  In 
some  cases  a  hole  about  one-eighth  of  an  inch  in  diameter  is 
drilled  down  the  centre  from  the  outside  of  each  stay,  but  not 
quite  through.  If  the  bolt  breaks,  water  will  escape  violently 
through  this  hole.  The  breakage  of  a  large  number  of  stays  at 
once  has  caused  some  frightful  catastrophes,  the  engine  often 
turning  a  somersault.  Inventors  have  not  been  idle,  and  various 
patents  have  been  taken  out  for  imparting  flexibility  to  the  bolts. 
These  as  a  rule  contemplate  a  reduction  in  the  sectional  area  of 
the  bolt.  One  inventor  cuts  four  slots  longitudinally  in  the  bolt. 
These  are  made  with  a  small  circular  saw,  and  the  slots  are 
deeper  in  the  middle  than  at  either  end.  The  ordinary  practice 
is,  however,  to  make  the  stays  on  the  same  principle  as  a  Palliser 
armour-plate  bolt,  a  principle  involving  so  much  and  of  such 
wide  application  that  it  claims  some  explanation  here. 


CHAPTER    XII 

STAY   BOLTS 

IN  the  early  days  of  armour  plating  the  targets  consisted  of 
beams  to  which  the  plates  were  fixed  by  bolts  about  3  inches  in 
diameter.  The  heads  were  tapered  and  counter-sunk  into  the 
plate.  The  screwed  ends  and  the  nuts,  under  which  large 
washers  were  placed,  were  inside  the  ship's  side,  so  to  speak. 
When  a  projectile  struck  the  plate  a  number  of  the  nuts  always 
flew  off,  the  bolts  breaking  through  the  threads ;  and  to  say 
nothing  of  the  mischief  they  were  quite  capable  of  doing  among 
a  crew,  it  was  only  necessary  to  hit  a  plate  two  or  three  times, 
and  it  would  fall  off  altogether.  Various  attempts  were  made  to 
get  over  this  radical  difficulty.  Elastic  washers  were  put  under 
the  nuts  with  indifferent  results.  Then  Captain  Palliser,  an 
artillery  officer,  solved  the  problem  by  reducing  the  diameter  of 
the  bolts  somewhere  about  the  middle.  A  reduction  in  section,  no 
matter  how  effected,  had  the  same  result.  Thus  boring  holes  down 
the  centre  of  the  bolts  had  the  same  effect  as  turning  them  down 
outside.  This  is  the  reason  why  the  crank  shafts  and  crank  pins 
of  marine  engines  are  hollow.  But  this  is  not  all.  The  effect  of 
cutting  a  screw  thread  on  a  bolt  is  about  the  same  as  if  it  were 
nicked  all  round.  Thus  an  armour  plate  bolt  being  screwed, 
would  in  effect  be  nicked,  and  would  break  generally  just  where 
the  last  thread  of  the  screw  joined  the  solid.  Captain  Palliser 
turned  his  bolts  down  in  such  a  way  that  the  screwed  part  was 
always  "  proud  "  of  the  rest  of  the  bolt.  Thus  if  the  thread  of  a 
3-inch  bolt  was  one-fourth  of  an  inch  deep,  then  the  body 
was  turned  down  until  it  was  something  less  than  2J  inches  in 
diameter.  In  most  cases  the  fire-box  stay  bolts  of  locomotives 
are  made  in  this  way,  but  it  is  doubtful  if  an  adequate  return  has 

E.L.  H 


98  THE  EAILWAY  LOCOMOTIVE 

been  obtained.  The  Palliser  principle  works  to  admiration  in 
dealing  with  sudden  stresses  or  shocks,  but  it  does  not  appear  to 
be  equally  efficacious  when  a  bar  under  steady  stress  is  bent 
frequently  through  very  small  angles.  At  all  events,  stay  bolts 
are  still  prone  to  break  ;  and  it  is  held  by  many  engineers  that 
the  best  chance  of  success  lies  in  providing  a  wide  water  space, 
which  gives  a  long  bolt,  and  making  the  bolts  thicker.  As  much 
as  1J  inch  over  the  threads  has  been  adopted  with  success. 
When  a  stay  is  renewed  it  is  almost  always  necessary  to  enlarge 
and  retap  the  holes,  and  then  stays  of  1J  inch  over  the  threads 
are  put  in.  In  the  United  State?  no  stay  bolts  less  than  |-  inch 
diameter  are  used  in  locomotive  fire-boxes,  and  then  only  for  150  Ibs. 
pressures.  Both  in  the  United  States,  in  this  country  and  on 
the  Continent  various  materials  have  been  tried.  In  America 
the  preference  is  given  to  treble-refined  iron,  but  then  copper 
boxes  are  almost  unknown  in  the  United  States,  mild  steel  taking 
the  place  of  the  more  expensive  metal.  In  this  country,  although 
steel  is  used  to  a  limited  extent,  it  has  not  met  with  general 
favour,  and  the  stay  bolts  are  almost  always  of  copper.  Various 
bronzes  have  been  tried,  and  for  the  lower  rows  of  bolts  bronze 
is  still  being  used  to  some  extent.  Lately  recourse  has  been  had 
again  to  Bowling  or  Lowmoor  Iron.  The  strength  of  a  fire-box 
is  largely  dependent  on  the  riveted  heads  of  the  stay  bolts,  and 
these  are  very  liable  to  be  worn  away  by  the  friction  of  the  fuel 
against  the  sides  of  the  box. 

It  is  worth  notice  that  although  theoretically  the  bending 
stresses  are  the  same  at  each  end  of  the  bolt,  yet  that  it  is  usually 
at  the  inside  of  the  outside  plate  that  fracture  occurs. 

The  pulling  stresses  on  the  bolts  are  Very  moderate.  Each 
has  to  support  an  area  of  4  by  4  =  16  square  inches.  With  a 
pressure  of  200  Ibs.,  this  gives  3,200  Ibs.  as  the  tension.  If  the 
bolt  has  been  turned  down  to  '601  inches  area  and  we  take  the 
ultimate  strength  of  copper  at  16  tons  or  35,840  Ibs.  per  square 
inch,  then  35,840  X  '601  =  21,600  Ibs.  as  the  breaking  strength 

of  each  bolt,  and      '        =  6*4  which  is  the  factor  of  safety  when 


the   boiler   is   new.     Apparently   this  is   enough,  but   as   it   is 


STAY  BOLTS  99 

unquestionable  that  deterioration  begins  from  the  first  day,  few 
engineers  regard  it  as  sufficient,  and  for  these  higher  pressures 
larger  diameters  or  closer  spacing  is  always  adopted.  Stays  as 
much  as  1 J  inches  diameter  spaced  3^  inches  centre  to  centre,  have 
been  used. 

How  long  a  stay  bolt  will  last  is  a  vexed  question.  According 
to  some  authorities,  long  before  fracture  is  likely  to  take  place, 
the  rivet  heads  will  have  been  worn  off  and  the  stay  begin  to 
leak.  A  great  deal  of  this  difference  of  opinion  seems  to  be  due 
to  varieties  in  the  quality  of  the  coal  used  on  different  lines, 
methods  of  firing,  and,  above  all,  the  characteristics  of  the  metal 
of  which  the  stay  is  made.  An  explosion  which  occurred  on  the 
Hull  and  Barnsley  Eailway  last  September  is  so  instructive  and 
bears  so  directly  on  what  has  just  been  said,  that  particulars  of 
it  may  well  find  a  place  here.  The  three  engravings,  Figs.  41,  42, 
43,  show  the  construction  of  the  fire-box  and  the  effect  of  the 
explosion.  The  crown  was  supported  by  sling  stays  G  G  for 
about  two-thirds  of  its  length.  Thence  onward  by  three  trans- 
verse bridge  stays,  E,  the  ends  of  which  rested  on  angle  irons 
riveted  to  the  inside  of  the  outer  fire-box  ;  the  water  spaces 
do  not  appear  to  have  been  more  than  2J  inches  wide.  The  fire- 
box seems  to  have  always  given  trouble,  no  matter  for  surprise 
when  the  great  depth  of  the  thin  sheets  of  water  at  the  sides  of 
the  box  are  considered.  Fig.  44  is  very  instructive,  showing  as 
it  does  how  the  inside  ends  of  the  stays  disappeared.  The 
riveted  heads  first  went,  then  leakage  took  place  and  caulking 
began,  and  the  unfortunate  stays  had  their  ends  beaten  down  in 
the  plate  until  they  lost  their  hold,  and  this  took  place  in  less 
than  two  years.  The  engine  (a  goods  tank)  was  standing  in  a 
siding  when,  about  3  a.m.,  it  exploded  ;  the  driver  who  was  on  the 
footplate  was  killed,  the  fireman  who  had  gone  to  a  signal  box  a 
little  way  off  was  not  hurt.  The  Board  of  Trade  report  states 
that  "  The  explosion  was  caused  by  the  failure  of  a  group  of 
stays,  about  30  in  number,  situated  near  the  bottom  of  the  left- 
hand  side  of  the  fire-box  in  the  2nd,  3rd,  4th,  and  5th  rows, 
counting  from  the  bottom,  the  attachment  of  which  to  the  copper 
plate  had  become  most  defective.  The  clenched  heads  of  these 

H2 


100 


THE  EAILWAY  LOCOMOTIVE 


STAY  BOLTS  101 

stays  were  completely  wasted  away,  and  this  part  of  the  fire-box 
side  was  in  consequence  dependent  for  support  on  the  screwed 
parts  of  the  stays  in  the  stay  holes,  but  owing  to  the  repeated 
hammering  and  caulking  of  the  ends  to  make  them  steam  tight 
the  threads  had  been  seriously  damaged  and  the  stays  had  become 
too  short,  the  ends  being  below  the  fire  surface  of  the  plate.  In 
this  condition  they  were  unable  to  support  the  plate,  and  the 
latter  was  forced  over  the  ends  in  the  form  of  a  bulge.  Once  the 
bulge  started  the  surrounding  part  of  the  plate  appears  to  have 
slipped  easily  and  rapidly  over  the  adjacent  stays,  many  of  which 
also  were  without  proper  heads,  the  scalding  steam  and  water 
escaping  through  the  stay  holes  into  the  fire-box  and  thence  to 
the  atmosphere.  When  the  bulge  had  extended  the  full  length 
of  the  side  of  the  fire-box  to  the  back  plate  and  tube  plate,  these 
crumpled  in  and  the  bulged  side  appears  to  have  begun  to  tear 
away  at  the  two  upper  corners  simultaneously,  and  after  com- 
pletely tearing  along  the  top,  it  was  driver;  downwards,  hinging 
along  a  line  level  with  the  top  edge  of  the  upper  row  of  rivets 
attaching  the  bottom  part  of  the  side  to  the  foundation  ring,  and 
it  appears  to  have  held  on  at  this  part  until  the  plate  itself  had 
bent  through  an  angle  exceeding  180  degrees  from  its  original 
position.  The  plate  was  then  blown  to  the  left-hand  side  of  the 
boiler,  its  flight  in  that  direction  being  due  to  the  bottom  edge 
remaining  attached  to  the  foundation  ring  until  the  last.  The 
failure  of  the  side  stays  described  above  occurred  with  extreme 
rapidity,  the  whole  operation  lasting  probably  less  than  a 
second." 


CHAPTER  XIII 


THE    FIRE-BOX 

WE  have  now  to  consider  more  in  detail  how  the  crown  sheet 
or  top  of  the  fire-box  is  supported.  In  the  older  type  of  engines 
the  outer  shell  is  always  semicircular.  The  metal  is  in  tension, 
and  no  staying  is  required.  Two  methods  of  supporting  the 
inside  box  have  been  mentioned.  The  first,  and  by  far  the  most 
common,  consists  in  bridging  the  top  with  girders,  and  slinging, 
so  to  speak,  the  crown  sheet  from  these  girders.  Formerly  the 

^ girders  were  always  made  each  of  two 

wrought  iron  flitch  plates,  riveted  to- 
gether with  distance  pieces  between. 
The  sling  bolts  came  up  between  them, 
and  the  nuts  were  carried  on  large 
washer  plates  spanning  both  bars.  In 
the  present  day  cast  steel  bars  are  used. 
These  have  nipples  on  them  which  are 


Slingbolt  -^ 


Fire 


FIG.  45.— Girder  stay. 


bored  and  tapped,  and  into  these  the  sling  bolts  are  screwed  as  at 
N  N,  Fig.  39.  The  ends  of  these  girders,  no  matter  how  they  are 
made,  are  extended  downwards  and  very  carefully  bedded  on  the 
fire-box  in  a  way  which  will  be  best  understood  from  the  sketch, 
Fig.  45.  In  most  cases — invariably  in  this  country — the  girders 
run  fore  and  aft  instead  of  transversely.  Seeing  that  the  shorter 
a  beam  is  the  stronger  it  is  for  a  given  section,  this  appears  to 
be  a  mistake.  The  long  girder  has  not  been  retained  without  a 
reason  however.  The  internal  fire-box  is  always  built  up  of  a 
single  sheet  of  copper — which  may  be  as  much  as  8  feet  wide  by 
18  or  20  feet  long— a  front  plate  known  as  the  tube  sheet,  and  a 
third  known  as  the  back  plate.  The  system  is  rendered  necessary 
by  the  fact  that  the  tube  sheet  is  nearly  twice  as  thick  as  any  of 


THE  FIEE-BOX  103 

the  other  plates.  The  back  plate  and  tube  plate  are  flanged 
inwards  all  round,  and  the  plate  forming  the  sides  and  crown  is 
riveted  over  these  flanges  in  the  way  shown  in  Fig.  45.  On  the 
flanges  rest  the  toes  of  the  girders,  which  transmit  their  load 
down  the  vertical  plates,  which  are  stiffened  by  the  stays  and 
the  tubes,  so  that  they  cannot  buckle.  Ultimately  in  this  way 
the  stress  is  transmitted  to  the  foundation  ring.  If  the  girders 
ran  across  they  would  find  no  adequate  bearing  for  their  toes ; 
but  besides  this,  as  holes  fitted  with  screw  plugs  are  provided  in 
the  upper  part  of  the  outside  back  plate,  clearing  rods  can  be 
passed  between  the  girders  to  remove  deposit  from  the  crown  of 
the  fire-box  in  a  way  that  would  be  impossible  with  the  trans- 
verse girder.  It  is  also  thought  that  the  circulation  in  the  boiler 
is  better  with  longitudinal  girders.  The  strength  of  these  girders 
is  generally  calculated  by  the  formula  for  a  beam  of  uniform 
section,  supported  at  each  end  and  carrying  a  distributed  load. 
Let  w  =  the  load  in  pounds, 

I)  =  breadth  of  beam  in  inches, 

d  =  depth  of  beam  in  inches, 

I  =  length  of  beam  in  inches, 

c  =  a  constant,  usually  16,000, 

mu  16,000  X  d2  X  b  r  i-    * 

Then  —j—         -  —  safe  load. 

Of  course  when  the  girder  consists  of  two  flitch  plates,  b  will 
equal  the  sum  of  their  thickness. 

The  reader  will  probably  have  noticed  that  many  of  the 
locomotives  of  the  Great  Western  and  Great  Central  Kailways 
have  boilers  with  large  rectangular  structures  over  the  fire-box. 
The  illustration  Fig.  46  of  one  of  Mr.  Churchward's  boilers 
(p.  104)  shows  this  very  clearly.  The  side  plates  of  the  outer  fire- 
box, instead  of  forming  a  semicircle  as  just  described,  are  carried 
up  and  united  by  a  flat  at  the  top,  in  so  far  representing  in  shape 
the  inside  fire-box.  This  design  was  the  invention  of  Mons. 
Belpaire,  a  Belgian  engineer,  and  it  possesses  several  advan- 
tages. It  gives  a  large  steam  space,  and  it  entirely  dispenses 
with  the  heavy  bridge  girders.  The  method  of  staying  is  the 
first  referred  to  on  p.  95.  The  crown  of  the  inside  fire-box 


104 


THE  EAILWAY  LOCOMOTIVE 


•3 
I 


THE  FIEE-BOX  105 

is  supported  by  screwed  stays  just  as  the  sides  are,  only  the  stays 
are  much  longer.  The  flat  sides  of  the  outer  box  are  supported 
by  transverse  stay  bolts.  Some  modifications  in  the  size  and 
arrangement  of  the  stays  have  been  introduced  by  different 
makers,  but  with  these  we  need  not  concern  ourselves. 

Attention  has  been  directed  to  the  prejudicial  action  of  expan- 
sion and  contraction.  It  is  the  usual  practice,  as  already  stated, 
to  tie  the  bridge  stays  each  by  two  slings,  P  P  (Fig.  39),  to  the 
semicircular  crown  of  the  fire-box.  However  tightly  these  may 
be  screwed  up  when  cold,  as  soon  as  the  box  is  heated,  by  rising 
it  leaves  the  slings  slack,  and  they  can  then  give  no  real  support. 
The  idea  is,  however,  that  they  prevent  the  gradual  crumpling 
down  of  the  front  and  back  plates  under  the  toes  of  the  girders, 
and  that  in  any  case  they  will  help  to  prevent  the  blowing  down 
of  the  crown  plate  should  the  side  stays  give  way  and  permit 
the  fire-box  plates  to  buckle  in.  It  does  not  appear,  however, 
that  there  is  any  recorded  instance  of  this.  When  a  crown 
collapses  the  girders  or  the  slings  break.  Unless  care  is  taken 
in  fitting  the  slings  they  may  do  much  harm.  It  is  right  to 
state  here,  however,  that  many  engineers  hold  that  the  rising  of 
the  inner  box  only  takes  place  when  steam  is  being  got  up,  and 
that  when  the  boiler  is  fully  heated  the  slings  to  the  roof  are 
again  tight.  But  the  fact  remains  that  the  co-efficient  of  the  expan- 
sion of  copper  being  much  greater  than  that  of  steel,  the  crown 
of  the  inner  box  must  be  higher  up  in  the  boiler  when  it  is  hot 
than  when  it  is  cold.  To  this  it  is  replied  that  the  outer  crown 
rises  a  little  by  expansion  while  the  roof  girders  spring  or  deflect 
downwards  a  little  under  the  load,  and  so  the  slings  come  into 
use.  Whatever  force  may  be  allowed  to  these  arguments  as 
mere  expressions  of  well  considered  opinion,  the  fact  seems  to 
remain  that  girder  sling  stays  prevent  the  gradual  crushing  down 
of  the  tube  plate,  which  in  process  of  time  makes  the  holes  oval 
and  renders  it  almost  impossible  to  keep  the  tubes  tight.  No 
doubt  the  parts  under  stress  fight  it  out  among  themselves  and 
adjust  their  differences.  We  may  take  as  proved  that  the  all  but 
universal  employment  of  these  girder  slings  is  not  the  result  of 
fashion  or  prejudice  ;  they  are  of  use  or  they  would  not  be  fitted. 


106  THE  EAILWAY  LOCOMOTIVE 

A  very  simple  boiler  has  been  made  by  slightly  curving  the  top 
of  the  inside  box  and  staying  it  directly  to  the  curved  top  of  the 
outer  box,  some  of  the  stays,  of  course,  radiating,  as  in  Fig.  41. 
But  the  stays  then  prevent  the  inner  box  from  rising  when 
expanding,  and  a  heavy  stress  is  put  on  the  foundation  ring, 
tending  to  buckle  the  plates  at  the  root  of  the  fire-box.  At  first 
sight,  the  Belpaire  arrangement  would  be  open  to  the  same 
objection,  but  it  is  not,  because  the  plates  are  flat  and  pliable, 
and  stresses  are  taken  just  as  they  should  be  taken.  Two 
objections  have  been  urged  against  the  Belpaire  design  ;  one  is 
that  it  is  very  ugly,  which  we  may  pass  over ;  the  other  is  more 
serious.  It  is,  that  the  external  fire-box  interferes  with  the 
driver's  view.  On  the  continent  the  objection  does  not  apply, 
because  a  footplate  at  least  a  foot  wider  than  that  which  the 
loading  gauge  permits  in  this  country  is  admissible. 

The  reader  is  referred  to  detailed  descriptions  of  the  locomotive 
for  information  about  the  various  methods  in  use  for  supporting 
such  plates  as  the  back  plate  above  the  inside  fire-box,  and  the 
smoke- box  tube  plate  above  the  tubes.  It  is  enough  to  say  here 
that  longitudinal  steel  bars  running  from  end  to  end  of  the 
boiler  in  the  steam  space  are  often  used. 

Mention  has  been  made  of  the  foundation  ring,  sometimes 
called  "the  bottom  rail,"  by  which  the  space  between  the  inside 
and  outside  fire-box  is  filled  up  at  the  bottom.  It  has  already 
been  shown  in  section,  Fig.  39.  It  is  in  the  present  day 
almost  invariably  a  rectangular  steel  casting  softened  by  anneal- 
ing. When  it  has  been  roughly  fitted  it  is  ground  all  over  to 
remove  scale  and  impart  a  true  surface.  It  is  put  in  place  and 
holes  are  then  drilled  through  it  and  the  inside  and  outside 
boxes,  and  rivets  subsequently  put  through  these  secure  the 
boxes  to  each  other;  afterwards  the  seams  are  caulked  on  the 
outside.  Foundation  rings,  if  well  made  and  fitted  and  properly 
riveted,  give  little  trouble. 

A  firing  hole  is  provided  in  both  the  inside  and  outside  fire 
box.  The  space  round  this  must  be  filled  up.  At  one  time, 
a  ring  precisely  similar  to  the  foundation  ring,  but  much 
smaller,  was  used  in  the  same  way,  see  Fig.  39.  For  some 


THE  FIEE-BOX 


107 


Firebox 


reason,  not  quite  clear,  the  inner  seam  between  the  copper  and 
the  ring  was  very  liable  to  leak.  One  improvement  consisted 
in  dishing  the  copper  plate,  so  that  only  a  thin  ring  was 
required.  This  checked  leaking,  but  the  copper  was  found  liable 
to  groove  or  crack  in  the  dished  part,  and  the  method  shown 
in  the  accompanying  sketch,  Fig.  47,  invented  by  the  late  Mr. 
Webb,  of  the  London  and  North  Western  Kailway,  finds  much 
favour.  The  inside  fire-box  is  bent  outwards  all  round  in  the 
form  of  a  truncated  cone.  The  back  plate  of  the  outside  box  is 
dished  in  like  manner  to  fit  it.  The  inside  fire-box  without  the 
foundation  ring,  can  be  dropped  in  as  far  for- 
ward as  it  will  go,  and  is  then  pushed  back 
until  the  inner  cone  slips  into  the  outer  one. 
A  special  tool  for  drilling  the  plates  in  place 
for  the  rivets  is  used. 

Some  diversity  of  opinion  exists  as  to  the 
quality  of  the  copper  in  a  fire-box.  Many 
engineers  specify  for  "  pure "  copper.  This 
appears  to  be  a  mistake,  for  pure  copper  is 
very  soft  and  will  not  withstand  the  attrition 
of  the  burning  coals.  The  consequence  is  that 
the  lower  parts  of  the  boxes  are  worn  thin,  and 
have  to  be  renewed.  It  is  a  much  safer  prac- 
tice to  specify  for  "  best"  copper,  which  is  by 
no  means  the  purest.  The  specification  in  use  on  the  London 
and  South  Western  Eailway  is  given  here. 

"  The  copper  is  to  be  of  the  very  best  quality  manufactured, 
and  to  be  of  the  exact  dimensions,  both  as  regards  form  and 
thickness,  as  given  on  the  drawings  or  list  supplied. 

"  The  copper  plates  are  to  be  properly  annealed,  and  a  piece 
taken  from  each  plate  must  stand  the  following  tests,  viz.  : — 

"  The  ultimate  tensile  strain  to  be  not  less  than  fifteen  tons 
per  square  inch,  with  an  elongation  of  not  less  than  40  per  cent, 
in  2  inches. 

"  A  piece  6  inches  long  is  also  to  be  bent  double  when  cold 
without  showing  signs  of  fracture  at  the  heel  of  the  bend. 

"  A  duplicate  test  piece  to  be  sent  to  Nine  Elms  to  be  tested. 


PIG.  47. 


108  THE  EAILWAY  LOCOMOTIVE 

"  Any  question  arising  must  be  referred  to  the  Chief  Mecha- 
nical Engineer,  whose  opinion  and  decision  are  to  be  taken  as 
final  and  binding." 

The  grate  H,  Fig.  39,  which  in  this  country  is  always  made 
of  thin  wrought  iron  or  steel  bars,  wedge  shaped  in  cross 
section,  is  carried  on  bearers,  resting  on  studs  screwed  into 
the  copper  box.  A  great  many  patents  have  been  taken  out  for 
improvements  in  grates,  and  some  of  very  ingenious  construc- 
tion are  in  use  in  other  countries.  They  are  usually  of  the 
"  rocking  "  type,  and  are  intended  to  break  up  slag,  and  keep 
the  air  spaces  clear.  They  are  not  used  in  this  country,  because 
the  coal  is  good  and  clean. 

Great  diversity  of  practice  exists  as  regards  fire  doors.  No 
two  railways  use  the  same  kind  of  door.  It  has  to  be  so  small 
that  the  amount  of  air  passed  through  the  fire  hole  can  be 
regulated,  and  it  must  be  under  the  control  of  the  driver  with 
one  hand,  as  he  opens  it  for  every  shovelful  of  coal  put  in  by 
the  fireman,  closing  it  again  immediately.  A  long  chapter 
might  be  written  on  fire  doors  alone,  the  quality  of  the  coal  and 
the  method  of  firing  mainly  determining  its  construction. 

In  the  early  years  locomotive  furnaces  had  no  ash  pans. 
The  dropping  of  red-hot  cinders  on  the  road  was  found  to  be 
objectionable,  and  a  plain  "  scoop  "  of  sheet  iron  was  placed 
under  the  box.  This  caught  the  cinders  ;  but  it  did  more,  its 
open  mouth  caught  the  air,  which  rushed  up  through  the  fire- 
bars and  greatly  promoted  combustion,  too  much  so  indeed. 
Then  a  flap  was  fitted  in  front,  controlled  by  a  rod  from  the 
foot-plate,  and  the  fireman  found  himself  provided  with  a  very 
efficient  means  of  regulating  the  draught.  When  the  engine  was 
standing,  by  closing  the  damper  he  could  save  fuel  and  prevent 
waste  of  steam.  But  further  experience  showed  that  the  ash  pan 
might  be  made  to  play  a  more  important  part.  The  combustion 
of  the  fuel  is  effected  partly  by  air  admitted  through  the  grate 
bars  and  partly  by  air  admitted  through  the  fire  hole.  The  latter 
is  regulated  by  the  fire  door,  the  former  by  the  ash  pan  damper. 
Long  since  the  ash  pan  became  a  somewhat  elaborate  con- 
trivance. In  the  United  States  the  dampers  are  sometimes  worked 


THE  FIEE-BOX  109 

by  steam  cylinders.  The  following  description  of  the  ash  pans 
designed  for  use  on  the  London,  Brighton  and  South  Coast  Rail- 
way is  taken  from  a  paper  which  was  read  before  the  Institution 
of  Civil  Engineers  by  Mr.  Stroudley.  Speaking  of  the  Gladstone 
class  of  express  engines  with  four  coupled  drivers  and  a  pair  of 
trailing  carrying  wheels  under  the  foot-plate,  he  said :  "  Care 
has  been  taken  to  provide  these  engines  with  means  for  effecting 
perfect  combustion  of  the  fuel,  and  to  prevent  the  emission  of 
sparks.  To  do  this,  they  have  been  fitted  with  an  air-tight  ash- 
pan,  which  has  an  angle  across  the  opening  for  the  damper  at 
the  back.  Water  is  allowed  to  escape  into  this  to  quench  the 
ashes,  and  so  keep  the  firebars  cool  and  in  good  order.  A 
deflector-plate  is  placed  across,  above  the  opening  for  the 
damper,  pointing  inwards,  and  this  throws  the  cinders  which 
fall  near  the  opening  towards  the  centre  of  the  ash-pan.  The 
opening  itself  is  covered  to  within  4J  inches  of  the  top,  with  a 
perforated  plate  mounted  on  hinges  ;  this  allows  the  air  to  pass 
into  the  ash-pan,  and  prevents  large  cinders  from  falling  out. 
A  damper,  having  a  handle  convenient  to  the  driver,  is  arranged 
to  shut  practically  air-tight,  giving  him  the  means  of  adjusting 
the  amount  of  air.  These  contrivances,  combined  with  the 
comparatively  extensive  grate  and  heating- surf  ace,  and  with 
large  blast  nozzle,  entirely  prevent  the  emission  of  sparks.  The 
ashes  carried  forward  into  the  smoke-box  would  pass  through  a 
sieve  having  ^-inch  mesh ;  the  average  quantity  being,  for  the 
heavy  passenger  or  goods  engines,  about  2J  cubic  feet  per 
100  miles  run." 

All  the  air  for  the  grate  is  admitted  at  the  back,  not  the  front, 
of  the  ash  pan. 

The  flue  tubes,  B  B,  Fig.  39,  which  run  through  the  boiler 
barrel,  are  usually  2  inches  in  diameter  and  8  to  11  feet  long  in 
this  country.  In  the  enormous  boilers  which  have  come  into 
vogue  in  the  United  States  they  are  14  to  20  feet  long  and  as 
much  as  3  inches  in  diameter. 

In  British  practice,  they  are  usually  spaced  f  of  an  inch 
apart.  In  some  boilers,  tubes  have  been  used  only  1J  inches  in 
diameter  inside,  spaced  but  f  inches  apart.  This  is  bad  practice, 


110  THE  KAIL  WAY  LOCOMOTIVE 

because  evaporative  efficiency  depends,  as  will  be  shown  when 
the  actual  working  of  a  boiler  is  dealt  with,  on  much  besides 
heating  surface.  The  late  Mr.  W.  Adams,  many  years  ago, 
when  locomotive  superintendent  of  tho  North  London  Railway, 
startled  the  world  by  introducing  1-inch  water  spaces — a  wholly 
unorthodox  innovation — with  2-inch  tubes.  Instead  of  losing  in 
power  his  boilers  steamed  much  better  than  before,  and  the 
tubes  did  not  leak. 

Flue  tubes  are  made  of  copper,  brass,  mild  steel,  or  mild  steel 
with  a  length  of  about  one  foot  of  copper  brazed  on  to  them. 
The  holes  in  the  smoke-box  tube  plate  are  always  bored  from 
^e  inch  to  J-  inch  larger  than  those  in  the  fire-box  tube  plate. 
The  leading  end  of  the  tube  for  a  length  of  2  or  3  inches  is 
swelled  out  to  fit  the  larger  hole ;  the  purpose  of  this  is  to  facili- 
tate the  taking  out  of  a  tube,  which  always  has  a  little  scale  on 
it.  This  will  pass  through  the  larger  hole. 

As  an  example  of  modern  practice  a  Lancashire  and  Yorkshire 
Eailway  tube  specification  is  given  here  :— 

"  Copper  tubes  must  be  solid  drawn  and  seamless,  perfectly 
sound  and  well  finished ;  free  from  surface  defects,  and  also 
capable  of  withstanding  expanding  and  bending,  without  show- 
ing the  least  sign  of  splitting,  or  cold  shortness.  The  ends  must 
ba  left  'hard,'  or  '  half  hard/  throughout,  because,  if  the  ends 
are  annealed,  the  junction  of  the  hard  and  soft  metal  becomes 
a  plane  of  weakness,  and  the  tube  invariably  collapses  there. 
The  thickness  must  be  10  I.  W.  G.  —  0*133  inches,  for  12  inches 
from  the  fire-box  end,  and  then  taper  from  10-12  I.  W.  G.  in 
a  length  of  18  inches.  The  remainder  parallel  12 1.  W.  G.  thick; 
to  be  swelled  -^  at  the  smoke-box  end  to  facilitate  withdrawal. 
The  weight  per  lineal  foot  is  as  follows : — 

"  DIAMETER  OUTSIDE. 

If  in.  ...  1-98  Ibs. 

If   „  ...  2*15    ,,  A  maximum  of  10  per  cent. 

1J-   ,,  ...  2*31    „  above  each,  and  5  percent. 

2     ,,  ..  2*47    „  under  will  be  allowed. 

aj  „    ...    2-68  „ 


THE   FIKE-BOX  111 

"  They  must  be  free  from  dirt  inside  and  out,  each  tube  must  be 
branded,  and  capable  of  sustaining  an  internal  pressure  of 
800  Ibs.  per  square  inch  and  an  external  pressure  of  250  Ibs. 
per  square  inch." 

As  to  the  popularity  of  various  materials,  the  author  is  indebted 
to  the  North  British  Locomotive  Co.,  Hyde  Park  Works,  Glasgow, 
for  the  following  facts.  Of  the  last  834  locomotives  built  by 
the  Company,  566  had  brass  tubes,  61  had  copper  tubes, 
89  had  steel  tubes,  118  had  iron  tubes.  On  the  Great  Western 
Eailway  mild  steel  tubes  have  been  used  exclusively  for  some 
years.  In  the  United  States  steel  or  iron  tubes  are  always  used. 

The  quality  of  the  tubes  and  the  way  in  which  they  are  fixed 
in  the  plates  is  of  very  great  importance.  The  leakage  of  tubes 
is  a  matter  of  almost  daily  occurrence,  and  when  it  is  at  all 
considerable  it  is  very  mischievous. 

For  many  years  the  tubes  were  always  fixed  in  the  same  way. 
They  were  put  in  place,  and  then  a  smooth  tapered  "  drift "  was 
hammered  into  them.  The  metal  was  in  this  way  expanded  and 
the  joint  between  the  tube  and  the  plate  made  good.  To  maintain 
tightness,  a  ring  called  a  ferrule,  about  2  inches  long  and  one- 
eighth  of  an  inch  thick,  made  of  wrought  iron  or  steel,  and 
slightly  tapered,  was  then  driven  into  the  tube.  The  smoke-box 
end  was  not  considered  to  need  ferrules,  because  it  was  of  iron, 
not  copper.  If  a  tube  leaked  afterwards  the  ferrule  was  driven 
in  a  little  further.  Sometimes  the  tubs  plate  was  cracked  in  this 
way  ;  more  often  a  tube  was  split.  It  was  no  uncommon  thing 
to  see  an  engine  running  with  a  dozen  tubes  plugged  at  each 
end  with  hard  wood  plugs,  which  were  carried  as  part  of  the 
tool-box  outfit.  The  "expander,"  invented  by  Mr.  Dudgeon, 
wrought  a  great  improvement.  The  expander  is  a  small  circular 
frame  in  which  are  put  a  number  of  little  hardened  steel  rolls. 
These  can  be  forced  apart  by  a  tapered  steel  drift.  The  tool  is 
provided  with  a  heavy  cross  handle,  by  which  it  can  be  caused 
to  revolve.  It  is  placed  in  the  end  of  the  tube,  the  drift  driven 
in  by  a  tap  with  a  light  hammer,  and  the  whole  turned  round 
by  the  cross  handle.  The  little  rollers  then  revolve  inside  the 
tube  and  literally  roll  out  the  metal,  expanding  the  tube  in  a  way 


112  THE  RAILWAY  LOCOMOTIVE 

quite  different  from  the  action  of  the  plain  drift,  and  hardly  ever 
splitting  a  tube.  Tube-fitting  in  this  way  has  become  a  very 
simple  and  straightforward  job,  requiring  little  skill,  while 
drifting  in  the  old  way  was  a  work  demanding  much  practice 
and  skill  if  the  result  was  to  be  satisfactory. 

If  instead  of  plain  rollers  grooved  rollers  are  used,  then  the 
tube  ends  can  be  swelled  out  on  both  sides  of  the  plate.  A 
beading  tool  on  the  same  principle  turns  over  the  end  of  the 
tube  and  so  prevents  it  from  being  pulled  through  the  plate. 
Ferrules  are  still  almost  always  used  at  the  fire-box  end,  not  to 
keep  the  tube  tight,  but  to  save  the  ends  from  destruction  by  the 
attrition  of  the  minute  hard  cinders  which  are  drawn  through 
by  the  powerful  draught. 

Tube  leakage  is  a  disease  from  which  the  locomotive  boiler  is 
very  likely  to  suffer.  It  is  due  to  expansion  and  contraction. 
The  tube  expands,  and  if  neither  the  fire-box  nor  the  smoke-box 
plates  will  give  way,  the  tubes  slip  in  the  holes.  They  are 
also  liable  to  expand  diametrically  to  such  an  extent  that  they 
dilate  the  holes  in  the  copper  tube  plate  beyond  the  elastic  limit 
of  the  metal.  The  result  is  that  when  they  cool  they  are  slack 
enough  in  the  holes  to  leak.  Various  methods  of  dealing  with 
longitudinal  expansion  have  been  tried.  One  used  by  the  late 
Mr.  W.  Stroudley  on  the  London  and  Brighton  Eailway  consists 
in  cambering  the  tubes  a  little  more  than  one  diameter.  Thus 
an  11  foot  tube,  2  inches  in  diameter,  would  be  uniformly  curved 
by  about  2J  inches.  When  the  tube  expanded  the  camber 
increased  for  reasons  sufficiently  obvious.  In  other  cases  the 
smoke-box  tube  plate  has  had  flexibility  imparted  to  it  by  making 
it  with  a  corrugated  ring  all  round.  The  best  and  simplest  plan, 
however,  consists  in  making  the  front  plate  so  large  that  a  good 
margin  exists  all  round  between  the  tubes  and  the  rivets  by 
which  it  is  attached  to  the  shell. 

The  accompanying  table  may  be  taken  as  representing  average 
practice  of  the  best  kind.  Some  makers  turn  out  rather  heavier, 
others  rather  lighter  boilers  with  almost  the  same  amount  of 
heating  surface.  It  must  not  be  forgotten  that  pressures  over 
180  Ibs.  remain  the  exception  and  not  the  rule.  Pressures  of 


THE   FIEE-BOX  113 

200  Ibs.  and  upwards  entail  difficulties  in  manufacture  and 
maintenance.  The  boilers  are  heavier  and  require  more  staying, 
and  they  wear  out  sooner  in  the  fire-box.  Altogether  it  remains 
a  disputed  question  whether  an  increase  of  pressure  above  180  Ibs. 
is  justified  commercially. 

WEIGHT  OF  LOCOMOTIVE  BOILERS. 

The  weights  given  are  of  complete  boilers  with  fire-bars,  but  without  any 
mountings. 

WORKING  PRESSURE  160  LBS.  PER  SQ.  INCH. 

Heating  surface 976  sq.  ft.  ..  1,592  sq.  ft.  ..  1,956  sq.  ft. 

tons  cwt.  tons  cwt.  tons  cwt. 

Weight  of  boiler  and  fire-bars     . .       10     10       .  .       12     10       . .       15     5 

WORKING  PRESSURE  170 — 180  LBS.  PER  SQ.  INCH. 

Heating  surface 1077  sq.  ft.  .  .  1,349  sq.  ft.  .  .  1,931  sq.  ft. 

tons  cwt.  tons  cwt.  tons  cwt. 

Weight  of  boiler  and  fire-bars     ..       10     10..       13      0        ..       170 


R.L. 


CHAPTEE  XIV 


THE    DESIGN    OF    BOILERS 

THE  smoke-box  appears  to  be  a  very  innocent  addition  to  the 
boiler ;  not  a  thing  about  which  much  controversy  can  exist,  yet 
it  may  be  doubted  if  any  other  portion  of  the  locomotive  has  been 
made  the  subject  of  keener  disputes,  or  more  varying  practice. 
For  a  full  explanation  of  the  reason  why,  the  reader  must  wait 
until  a  consideration  of  the  locomotive  at  work  comes  up.  For 
the  moment  it  must  suffice  to  point  out  that  it  is  of  extreme 
importance  that  sparks  should  not  be  ejected  up 
the  chimney  which  might  set  fire  to  crops  at 
the  roadside  in  dry  weather ;  while  on  the  con- 
struction of  the  box,  and  on  what  is  inside  it> 
depends  in  considerable  measure  the  economy 
or  the  reverse  of  the  boiler. 

Usually  the  front  tube  plate  and  the  front 
plate  of  all  are  rectangular  below,  and  they 
rest  on  the  cylinder  castings  when  these  are 
inside;  or  they  are  united  by  a  flat  horizontal  plate.  The  bottom 
of  the  box  is  always  filled  in  with  fire  bricks,  set  in  fire  clay, 
on  which  the  hot  cinders  and  ashes  which  come  through  the 
flue  tubes  are  deposited.  The  boiler  is  invariably  secured  in 
the  side  frames  at  the  smoke-box  end.  This  is  done  in  various 
ways,  but  it  is  always  done.  The  fire-box  is  fitted  with  two 
angle  steels  riveted  to  it.  The  heads  of  the  stay  bolts  in  the 
wake  of  the  side  plates  are  countersunk  to  form  a  flush  surface, 
or  holes  are  drilled  in  the  angle  so  as  to  fit  over  the  stay  bolt- 
heads,  and  the  fire-box  outer  shell  fits  closely  between  the  frames, 
to  which  are  also  riveted  two  angle  steels  on  which  those  of  the 
boiler  rest,  as  shown  in  the  sketch,  Fig.  48.  A  few  bolts  passing 


Side  Frame 


FlG.  48. 


UNIVERSITY 

of 

THE   DESIGN   OF  BOILERS  115 

through  oval  holes  and  a  slack  fit  are  sometimes  put  through  the 
angle  irons,  or  a  species  of  clip  is  put  over  both.  As  the  boiler 
expands  and  contracts  the  angle  steels  on  the  fire-box  slide 
backwards  and  forwards  on  those  on  the  frames  and  straining  is 
thus  avoided. 

To  large  numbers  of  boilers  domes  are  fitted.  These  are  short 
cylinders  of  steel,  with  tops  bolted  to  them,  sometimes  made  of 
cast  iron,  sometimes  dished  out  of  steel  plates.  The  domes  have 
large  curved  flanges  at  the  bottom,  by  which  they  are  riveted  to 
the  barrel.  As  a  large  hole  is  cut  out  in  the  barrel,  a  strengthening 
ring  is  fitted  inside  and  the  rivets  pass  through  the  three 
thicknesses  of  plate. 

In  some  cases  the  dome  is  made  large,  and  is  regarded  as  an 
important  factor  in  providing  steam  space.  The  steam,  too,  was 
always  taken  off  by  an  internal  steam  pipe  which  opened  higher 
up,  above  the  general  water  level  in  the  dome.  The  modern  big 
engine  boiler  is  so  high  that  there  is  no  room  for  a  high  dome, 
and  that  which  is  used  plays  rather  the  part  of  a  convenient 
casing  for  the  regulator  valve  than  an  addition  to  the  steam 
space. 

In  the  designs  of  boilers  considerable  differences  exist.  So 
long,  however,  as  they  are  of  moderate  size,  that  is  to  say,  with 
a  heating  surface  of  1,200  to  1,400  square  feet,  and  grates  with 
18  square  feet  or  so  of  surface,  they  are  all  very  much  alike. 
The  standard  modern  English  locomotive  is  of  the  4 — 4  type, 
that  is  to  say,  it  has  a  four-wheeled  bogie  in  front,  and  four 
coupled  driving  wheels ;  the  cylinders  are  18  or  18J  inches 
diameter,  the  stroke  26  inches,  and  the  working  pressure  160  Ibs. 
The  driving  wheels  are  6  feet,  or  6  feet  6  inches  in  diameter ; 
the  side  coupling  rods  about  8  feet  long.  Between  these  there  is 
no  difficulty  in  getting  in  a  fire-box  6  feet  long.  Mr.  Drummond, 
chief  mechanical  engineer  of  the  London  and  South  Western 
Eailway,  has  not  hesitated  to  use  side  rods  ten  feet  long,  and 
they  have  been  quite  successful. 

The  shape  of  the  internal  box  is  modified  by  various  considera- 
tions which  have  greater  or  less  weight  with  different  designers. 
The  normal  outer  box  for  engines  of  the  4 — 4  type  cannot  have  a 

i2 


116  THE  EAILWAY  LOCOMOTIVE 

greater  width  at  the  bottom  where  the  grate  rests  than  4  feet 
1  inch,  the  gauge  being  4  feet  8J  inches.  If  from  this  we  deduct 
the  thickness  of  four  plates,  the  inside  and  outside  fire-box,  two  at 
each  side — say,  2J  inches,  we  have  left,  allowing  a  3  J  inch  water 
space  at  each  side,  3  feet  2^  inches  for  the  width  of  the  grate ; 
with  a  2^  inch  water  space  it  may  be  3  feet  3J  inches  wide.  By 
reducing  clearance,  a  little  here  and  a  little  there,  the  absolute 
width  of  the  box  may  be  slightly  increased  so  as  to  give  a  grate 

3  feet  4  inches  wide  with  a  2J  inch  water  space.     The  idea  is,  of 
course,  to  get  the  largest  grate  area  possible,  but  it  will  be  shown 
further  on  that  an  increase  or  decrease  of  two  or  three  inches  in 
the  width  of  a  grate  is  of  no  importance,  while  an  extra  inch 
given  to  the  water  space  may  be  of  the  utmost  value.     There  is, 
indeed,  excellent  reason  to  believe  that  when  pressures  of  200  Ibs. 
or  over  are  used,  the  water  spaces  should  in  no  case  be  less  than 

4  inches  wide.     It  has  been  shown  already  that  the  longer  the 
stay  bolts  are  the  better,  because  they  are  more  flexible.     But  it 
is  imperative  that  the  circulation  of  water  should  be  thoroughly 
efficient   to   prevent    the    plates    from    becoming    over-heated. 
Copper,  there  is  every  reason  to  believe,  deteriorates  in  quality 
when  exposed  for  long  periods  to  severe  stresses  when  heated. 
The  metal  is  always  hotter  than  the  water  in  the  boiler ;  the 
temperature  proper  to  240  Ibs.,  absolute — 225  Ibs.  safety  valve 
pressure — is  397°  F.      That  of  the  inner  face  of  the  plate  is 
perhaps    twice   this,    and   may   be   much    more    unless    fairly 
"  solid  "  water  in  rapid  movement  is  in  the  water  space. 

So  far  the  fire-box  has  been  spoken  of  as  though  it  was  in  all 
respects  rectangular  with  the  exception  of  the  bending  at  the 
corners.  This  view  is,  however,  incorrect,  if  we  except  very 
small  locomotives.  It  has  been  pointed  out  that  the  width  of  the 
lower  portion  of  the  external  fire-box  cannot  much  exceed  4  feet, 
while  that  of  the  internal  box  can  only  be  about  3  feet  3  inches. 
If  now  the  inner  box  were  carried  up  straight  it  would  be 
impossible  to  get  in  a  sufficient  number  of  flue  tubes  ;  accordingly, 
the  inner  box  is  wider  at  the  top  than  the  bottom,  and  in  this 
way  a  barrel  even  5  feet  in  diameter  can  have  all  the  tubes  it  will 
accommodate,  say  300,  put  in. 


THE  DESIGN  OF  BOILEKS  117 

But  this  is  not  all.  The  enormous  engines  now  in  use  are 
fitted  with  grates  as  much  as  9  feet  long.  These  must  be  placed 
over  the  axle  of  the  last  pair  of  wheels  and  with  this  object  the 
grate  is  made  in  two  portions,  one  horizontal,  next  the  fire  door, 
and  the  other  steeply  inclined.  The  fire-boxes  inside  and  out 
are  cut  to  fit.  This  is  very  clearly  seen  in  the  photograph  of  a 
Great  Western  boiler  on  page  104.  In  certain  cases  the  front 
portion  only  of  the  box  is  curved,  the  width  required  to  accom- 
modate the  tubes  being  obtained  by  "  pocketing  out  "  the  side 
sheets.  The  advantage  is  that  more  water  space  is  left  in  the 
"  legs  "  at  each  side.  It  is  essential  in  some  respects  that  when 
a  boiler  is  large  the  fire-box  should  be  deep.  Now  for  reasons 
that  will  be  explained,  sunken  or  deep  boxes  do  not  make  steam 
as  freely  as  shallow  boxes.  To  improve  the  deep  box,  Mr.  Dugald 
Drummond,  Chief  Mechanical  Engineer  of  the  London  and  South 
Western  Eailway,  some  years  ago  put  transverse  water  tubes  into 
the  fire-box,  an  experiment  which  answered  so  well  that  a 
large  number  of  the  most  powerful  express  engines  on  the  line 
have  been  fitted.  A  cross  section  of  a  fire-box  is  given  on  page 
118,  Fig.  49.  The  tubes  A  A  are  of  very  mild  steel  set  on  a  slight 
incline,  and  are  "  rolled  "  into  the  inner  box  side  plates  just  as 
though  they  were  flue  tubes.  Access  is  got  to  them  by  doors  at 
each  side.  These  doors  are  carried  on  hinges  for  convenience, 
but  the  hinges  have  nothing  to  do  in  the  way  of  securing  them. 
The  doors  are  made  with  faced  joints,  which  are  bolted  to  steel, 
faced,  rectangular  castings  B  B  bolted  in  their  turn  to  the  outside 
of  the  fire-box  shell.  Through  a  certain  number  of  tubes  are 
passed  stay  bars  C  C  so  that-  the  outer  shell  is  properly  braced. 
It  can  be  proved  that  if  a  tube  containing  water  is  put  on  a  slight 
incline,  say  one  inch  to  the  foot  or  even  less,  provided  it  is  not 
more  than  twenty-four  diameters  long,  it  cannot  be  over-heated, 
the  circulation  within  being  very  ample.  The  endurance  of  the 
Drummond  tubes  seems  to  be  almost  phenomenal.  Their  average 
life  is  eight  years  and  two  months  and  their  average  mileage  is 
306,992.  After  200,000  miles  they  are  clean  inside  and  as  good 
as  new,  and  this  although  they  are  exposed  to  the  highest 
temperature  in  the  fire-box,  which  nearly  approaches  that  of  a 


118 


THE  EAILWAY  LOCOMOTIVE 


steel  melting  furnace.     In  the  section  it  will  be  seen  that  bridge 
girders  are  not  used.     The  crown  of  the  fire-box  is  slung  to  the 


CROSS  SECTION    OF  FIREBOX 

FIG.  49. — Drummond's  water  tube  fire-box. 

outer  roof  plate.  But  it  will  also  be  seen  that  the  slings  being 
in  couples  and  fitted  with  nuts  resting  on  cross  pieces,  the 
internal  fire-box  is  quite  free  to  rise  when  the  fire  is  first  lighted, 
simply  lifting  the  nuts  off  the  cross  bars.  With  the  advent  of 


THE  DESIGN  OF  BOILERS  119 

pressure  the  nuts  come  down  again  to  their  bearings.  In  this 
way  the  principal  objection  to  the  sling  stay  is  removed. 

One  other  type  of  fire-box  has  to  be  described.  In  this  country 
the  best  coal  in  the  world  is  available  for  locomotives,  and  we 
have  as  yet  built  but  a  few  boilers  which  can  compete  in  dimen- 
sions with  those  of  some  freight  engines  in  the  United  States. 
So  long  as  the  fire-box  is  placed  between  the  frames,  the  maximum 
grate  area  cannot  well  exceed  28  square  feet.  This  means  a 
grate  nearly  9  feet  long,  which  is  not  easily  fired.  In  Belgium 
much  of  the  locomotive  fuel  is  "  dead  slack."  It  is  little  more 
than  coarse  dust,  and  being  moistened  it  is  not  much  unlike 
black  mud.  This  is  burned  by  being  spread  out  thinly  on 
enormous  grates — as  much  as  70  square  feet  in  a  few  cases — 50 
square  feet  is  quite  common.  Engines  may  be  much  wider  in 
Belgium  than  in  Great  Britain,  because  Belgian  platforms  either 
do  not  exist  at  all  or  are  very  low.  The  fire-box  does  not  go 
between  the  frames  but  rests  on  top  of  them.  A  width  of  as 
much  as  9  feet  being  given  to  the  external  fire-box,  grates  6  feet 
wide  and  9  feet  long  become  possible.  There  are  two  fire  doors 
because  the  grate  could  not  be  kept  covered  from  one.  In  this 
country  a  few  locomotives  of  the  "  Atlantic  "  or  4 — 4 — 2  type 
have  been  built  in  which  the  external  fire-boxes  are  about  6  feet 
wide.  The  grates  stand  over  the  trailing  wheels,  which  are  of 
comparatively  small  diameter.  The  details  of  construction  do 
not  demand  any  special  description.  They  are  in  all  respects 
similar  to  those  already  dealt  with. 

Incidentally,  it  may  be  mentioned  that  various  attempts  have 
been  made  to  get  rid  of  the  flat-sided  firebox.  Thus  circular 
corrugated  furnaces  similar  to  those  in  a  marine  boiler  have 
been  tried  on  various  railways  with  but  moderate  success.  It 
is  very  improbable  that  the  normal  box  will  be  displaced  by 
innovations. 

It  is  assumed  that  the  reader  has  now  formed  an  adequate 
conception  of  not  only  what  the  locomotive  engine  boiler  is,  but 
why  it  is  what  it  is.  We  have  next  to  consider  what  it  does,  the 
nature  of  the  work  it  performs,  and  how  it  does  it.  It  is  worth 
while,  however,  to  repeat  that  there  is  no  other  type  of  steam 


J20  THE  EAILWAY  LOCOMOTIVE 

generator  so  suitable  for  being  carried  about  the  country  at  a 
high  speed  on  a  wheeled  vehicle.  Into  none  others  could  so 
much  heating  surface  be  put  of  just  that  kind  best  fitted  to  absorb 
the  energy  of  a  furnace  working  at  a  temperature  not  attained 
in  any  other  boilers,  save  those  of  torpedo  boats,  and  giving  off 
huge  volumes  of  intensely  hot  gas.  It  is  not  so  much  that  the 
locomotive  boiler  is  excellent,  as  because  it  is  the  only  practic- 
able boiler  that  it  enjoys  universal  favour.  It  is  in  nowise  too 
much  to  say  that  it  is  to  the  locomotive  boiler  we  owe  the  success 
of  the  railway  systems  of  the  world. 


CHAPTER  XV 

COMBUSTION 

IT  is  advisable  here  for  the  sake  of  completeness  to  put  before 
the  reader  a  few  general  facts  concerning  combustion.  They 
ought  to  be  known,  although  they  are  little  considered  in  the 
everyday  life  of  a  railway. 

The  burning  of  coal  means  the  chemical  combination  of 
oxygen,  carbon  and  hydrogen,  with  the  evolution  of  heat, 
carbonic  oxide,  and  water  in  the  form  of  steam.  With  the  various 
other  combinations  of  carbon,  hydrogen,  and  oxygen,  which  take 
place  we  need  not  here  concern  ourselves.  They  have  interest, 
of  course,  for  the  chemist,  but  not  for  the  locomotive  superinten- 
dent, the  engine  driver  or  fireman. 

In  most  text-books  it  is  taught  that  the  whole  of  the  energy 
comes  from  the  coal,  in  which  it  has  been  stored  up  by  the  sun's 
rays  acting  on  trees  and  plants  millions  of  years  ago,  but  no 
attempt  is  made  to  say  how  energy  exists  in  the  inert  black 
substance.  That  remains  one  of  the  insoluble  mysteries  of 
nature.  It  may,  however,  not  be  out  of  place  to  advance  here 
the  theory  that  the  energy  does  not  reside  in  the  coal,  but  in 
the  gas  with  which  it  combines.  Thus  the  molecular  energy— 
that  is  to  say,  the  energy  due  to  the  motion  of  its  molecules — is 
much  greater  in  oxygen  than  it  is  in  carbonic  acid  gas.  But 
this  gas  is  the  result  of  the  combination  of  oxygen  with 
the  carbon.  The  difference  appears  as  heat.  If  we  turn  to 
hydrogen,  we  find  that  probably  of  all  known  substances  it  pos- 
sesses the  highest  molecular  dynamic  energy.  Accordingly,  when 
it  combines  with  oxygen,  water  is  formed  which  has  little  or  no 
molecular  energy,  and  the  result  is  the  liberation  of  the  largest 
quantity  of  heat  that  can  be  obtained  by  direct  combustion. 


122 


THE  EAILWAY  LOCOMOTIVE 


Leaving,  however,  the  region  of  theory  and  turning  to  that 
of  fact,  the  following  figures,  which  show  the  heat  of  combustion 
with  oxygen  of  one  pound  each  of  the  substances  named,  in 
British  thermal  units  are  given,  and  also  what  is  perhaps  more 
to  the  point,  in  pounds  of  water  evaporated  from  and  at 
212°  F.  The  required  weight  of  oxygen  is  also  given.  The  figures 
are  the  result  of  a  series  of  experiments  carried  out  by  MM.  Favre 
and  Silbermann  some  sixty  years  ago.  Certain  corrections  have 
been  made  since,  but  they  are  unimportant  refinements. 


Combustible. 

Pounds  of 
Oxygen. 

Pounds  of 
Air. 

Total 
B.T.U. 

Evaporation. 

Hydrogen  gas    

8 

36 

62,032 

64-2  Ibs. 

Carbon    imperfectly 
burned  to  CO  

H 

6 

4,400 

4-55  ,, 

Carbon      completely 
burned  to  C02 

2§ 

12 

14,500 

15  „ 

Kanldne  deduced  from  these  figures  the  following  formulae 
for  general  application  :— 

Let  C  H  and  0  be  the  fractions  of  one  pound  of  the  compound 
which  consists  respectively  of  carbon,  hydrogen  and  oxygen,  the 
remainder  being  nitrogen,  ash,  and  other  impurities.  Let  h  be 
the  total  heat  of  combustion  of  one  pound  of  the  compound  in 
B.T.U.  Then 

h  =  14,500  j  C  +  4-28  (H  -  %)]  (1) 

I  \  vJ  ) 

Let  E  denote  the  theoretical  evaporative  power  of  one  pound 
of  the  compound  in  pounds  of  water  evaporated  from  and  at 
212°  F.  Then 


The  facts  of  interest,  as  concerned  with  locomotive  perform- 
ance, are  mainly  that  combustion  should  be  so  carried  on  that 
no  CO  shall  be  made.  This  end  can  be  attained  in  theory  with 
ordinary  coal  by  admitting  a  minimum  of  12  Ibs,  of  air  per 


COMBUSTION  123 

pound  of  coal.  In  practice,  however,  no  complete  union  of  all 
the  oxygen  can  be  obtained ;  and  the  minimum  quantity  of 
air  requisite  is  about  18  Ibs.  per  pound  of  coal.  At  62°  this 
would  occupy  a  volume  of  about  235  cubic  feet ;  then  if  a  loco- 
motive is  running  at  60  miles  an  hour  and  burning  30  Ibs. 
of  coal  per  mile,  the  volume  of  air  admitted  to  the  fuel 
will  not  be  less  than,  in  round  numbers,  7,000  cubic  feet. 
But  at  2,000°  F.  a  pound  of  air  occupies  62  cubic  feet, 
instead  of  13  cubic  feet,  and  so  the  volume  which  has  to  be 
withdrawn  from  the  fire-box  through  the  tubes  is  not  less 
than  33,480  cubic  feet  per  mile  and  per  minute.  Inasmuch, 
however,  as  the  gas  is  rapidly  cooled  in  its  passage  through 
the  tubes,  it  contracts  in  them,  and  thus,  although  33,480 
cubic  feet  enter  at  the  fire-box  end  of  the  tubes,  probably  not 
more  than  16,000  or  17,000  are  delivered  into  the  smoke-box. 

It  must  be  carefully  borne  in  mind  that  these  figures  are 
simply  approximations.  They  are  based  on  the  weight  of  air 
used  and  do  not  include  the  volume  of  CO,  for  example,  which 
replaces  an  equivalent  volume  of  air.  They  are  given  here  only 
in  order  that  some  idea  may  be  formed  of  the  quantities  which 
must  be  dealt  with  in  the  ordinary  working  of  a  locomotive 
engine.  Thus  we  see  that  while  some  33,000  cubic  feet  have  to 
get  into  the  tubes,  only  about  17,000  have  to  get  up  the  chimney. 
In  order  that  this  end  may  be  attained  means  must  be  provided 
for  exhausting  the  smoke-box,  so  that  the  external  pressure  of 
the  atmosphere  under  the  grate  bars  and  at  the  fire  door  may  be 
greater  than  that  at  the  top  of  the  chimney.  This  result  is 
secured  by  turning  the  exhaust  steam  from  the  cylinders  up  the 
chimney.  It  was  the  employment  of  the  exhaust  in  this  way 
that  enabled  the  "  Rocket  "  to  beat  all  its  competitors  at  the  Eain- 
hill  trials  ;  and  a  very  keen  discussion  at  one  time  took  place  as 
to  who  invented  a  device  which  has  proved  of  crucial  importance 
to  the  railway  system.  Indeed,  it  is  in  no  way  second  in  value 
to  the  tubular  boiler,  which  without  the  blast  pipe  would  be 
useless.  It  is  true  that  forced  draught  by  means  of  a  fan  might 
have  been  adopted ;  but  it  could  not  compare  in  general 
efficiency  and  activity  with  the  blast  pipe.  What  the  blast  pipe 


124  THE  EAILWAY  LOCOMOTIVE 

is,  and  how  it  works,  will  be  considered  when  we  come  to  the 
smoke- box.  The  two  original  claimants  for  its  invention  were 
Davie  Giddies,  a  friend  of  Trevithick,  and  George  Stephenson. 
The  honour  of  inventing  it  is  also  claimed  for  Trevithick  him- 
self. In  the  "  Life  of  Kichard  Trevithick,1'  written  by  his  grand- 
son, Francis  Trevithick,  published  in  1872  by  Messrs.  Spon, 
will  be  found,  on  p.  154  of  Vol.  L,  a  letter  which  refers  to  a 
locomotive  for  common  roads,  which  was  built  to  Trevithick's 
designs  in  1802.  A  passage  in  this  letter  has  been  construed  to 
mean  that  the  exhaust  steam  was  used  to  produce  a  draught ; 
but  as  it  stands  the  passage  is  quite  unintelligible.  On  p.  125, 
however,  of  this  volume  is  a  description  of  the  famous  Camborne 
engine,  the  first  locomotive  that  ever  conveyed  passengers,  and 
we  are  told  that  "  The  exhausted  steam  having  done  its  work  in 
the  cylinder  at  a  pressure  of  60  Ibs.  to  the  inch,  passed  into  the 
chimney  as  a  steam  blast  causing  an  intensely  hot  fire,  and  in 
its  passage  it  heated  the  feed  water." 

There  is  reason  to  believe,  however,  that  it  was  in  no  sense 
any  one's  invention.  The  obvious  way  to  get  rid  of  the  exhaust 
is  to  turn  it  up  the  chimney.  Thus,  leaving  Trevithick  out,  it 
is  known  that  this  had  already  been  done  in  Hackworth's  engine 
of  the  "  Puffing  Billy  "  type.  Its  action  in  promoting  combustion 
in  the  "  Eocket "  seems  to  have  been  a  discovery  rather  than  the 
result  of  a  direct  act  of  invention.  It  is  of  interest  to  add  that 
it  is  fairly  certain  that  the  knowledge  that  a  steam  jet  would 
entrain  air  and  so  induce  a  draught  was  possessed  by  the  old 
Greeks  and  Egyptians.  More  to  the  point,  however,  is  the  fact 
that  in  1594  Sir  Hugh  Platt  published  an  enquiry  and  a 
description  of  "  a  round  ball  of  copper  or  of  latten  (brass)  that 
blowes  the  fyre  verie  stronglie  by  the  attenuation  of  water  into 
ayre."  The  ball  or  balls  were  to  be  "  hung  in  the  chimney 
directly  over  the  fyre  to  cure  smoky  chimneys,  for  being  so  hung 
the  blast  arising  from  them  carries  the  loitering  smoke  along 
with  it." 

For  many  years  after  railways  began  to  play  an  important 
part  in  the  world's  work  locomotives  were  fired  with  coke.  Most 
of  the  railway  companies  manufactured  their  own  coke.  Fifty 


COMBUSTION  125 

years  ago  coke  ovens  still  existed  near  New  Cross,  the  property 
of  the  South  Eastern  Eailway  Company.  It  was  just  the  fuel 
for  the  locomotive  boiler.  The  tubes  kept  clean,  there  was  no 
smoke  and  no  soot.  It  was  believed  that  flame  could  not  pass 
through  a  tube  only  1|  inches  or  2  inches  in  diameter,  and  coke 
made  little  flame.  Engines  on  the  best  lines  were  spotlessly 
clean.  Drivers  and  firemen  wore  white  clothes  in  summer. 
When  the  steam  was  shut  off  the  supply  of  air  diminished  and 
much  carbonic  oxide  was  evolved.  This  escaping  up  the  chimney 
at  a  high  temperature  caught  fire  the  moment  it  reached  the 
outer  air.  At  night  engines  arriving  at  say,  Eugby,  came  in 
with  a  long  trail  of  lambent  blue  flame  from  their  funnels.  The 
sight  was  pretty,  but  not  comforting  to  those  whose  luggage  was 
stowed,  as  was  then  the  custom,  on  the  roofs  of  the  carriages. 

Coke  was  an  expensive  fuel,  and  about  the  year  1860  a  deter- 
mined effort  was  made  to  substitute  coal  for  it.  Patents  were 
taken  out  by  the  dozen,  and  large  sums  of  money  were  expended 
by  the  railway  companies  with  very  indifferent  success.  They 
could  not  burn  bituminous  coal  without  sending  torrents  of 
smoke  into  the  air,  and  the  engines  did  not  make  steam.  The 
trouble  was,  however,  at  last  got  over  by  very  simple  means. 
Across  the  fire-box  was  thrown  a  fire  brick  arch  supported  at  the 
ends  on  studs  screwed  into  the  copper  plates,  as  shown  at  F 
in  Fig.  39.  The  forward  face  of  this  arch  came  below  the  ends 
of  the  tubes.  The  rear  side  was  pitched  rather  above  the  level 
of  the  top  of  the  fire  door.  Into  the  fire  hole  was  fitted  a  sheet 
iron  scoop  deflector,  G,  Fig.  39.  When  the  train  was  running, 
the  fire  door  was  left  partly  open,  and  the  ash-pan  dampers  were 
more  or  less  closed.  The  products  of  combustion  could  no  longer 
rush  straight  into  the  tubes.  They  had  to  curl  backward  to  get 
to  the  upper  side  of  the  bridge.  Now  the  bridge  very  quickly 
became  white  hot,  and  kept  up  the  temperature  of  the  gases ; 
but  these  encountered  a  rush  of  air,  which  the  scoop  beat  down 
on  them  and  the  surface  of  the  blazing  coal  below.  The  result 
was  that  the  space  above  the  brick  arch  became  full  of  a  brilliant 
white  flame,  and  no  smoke  worth  mentioning  came  out  of  the 
chimney. 


126  THE  RAILWAY  LOCOMOTIVE 

With  various  modifications,  principally  in  the  construction  of 
the  fire  door  and  of  the  bridge,  as  for  example  the.  use  of  toggled 
instead  of  plain  wedge-shaped  bricks,  this  is  the  system 
invariably  adopted  on  all  railways  everywhere  to-day  where  coal 
is  burned  with  a  minimum  of  smoke.  The  arrangement  is 
represented  diagrammatically  in  Fig.  39. 


CHAPTER  XVI 

FUEL 

IT  would  be  mere  waste  of  space  to  reproduce  here  any  of  the 
elaborate  tables  which  have  been  prepared  from  time  to  time 
setting  forth  the  constituents  of  coal.  The  railway  companies 
purchasing  coal  by  the  100,000  tons  at  a  time  do  not  much 
concern  themselves  with  analysis  unless  coal  from  a  new  seam 
should  be  brought  to  their  notice.  The  locomotive  super- 
intendents purchase  particular  coals  or  leave  them  alone  as  the 
result  of  experience ;  and  the  selection  is  based  on  quite  other 
considerations  than  a  chemical  analysis,  which  might  be  quite 
misleading.  Nevertheless,  on  all  the  great  railways  coal  testing  is 
continually  carried  on  in  the  laboratories  as  a  check  on  the  results 
of  practice,  and  to  make  it  as  certain  as  the  analytical  chemist 
can  that  the  companies  get  full  value  for  their  money.  Various 
characteristics  of  the  coal  have  to  be  kept  in  mind,  and  as  a  good 
deal  of  misconception  appears  to  exist,  it  is  worth  while  here  to 
state  the  facts  as  they  are. 

Coal  is  only  a  means  to  an  end.  That  end  is  the  production 
of  steam.  The  price  paid  by  the  railway  company  for  its  steam 
depends  largely,  but  of  course  not  altogether,  on  the  performance 
of  the  coal.  Let  us  suppose  that  a  given  coal  costs  ten  shillings 
a  ton,  and  that  it  is  so  good  that  each  ton  of  it  will  make  ten 
tons  of  steam. 

A  different  coal  is  to  be  had,  however,  which  will  make  only 
eight  tons  of  steam  per  ton.  This  coal  it  will  be  said  is  inferior 
to  the  first.  So  it  is  in  one  sense,  but  it  may  be  selected  notwith- 
standing by  the  railway  company  because  it  costs  only  seven 
shillings  a  ton.  With  the  expensive  coal  seven  shillings  will 
only  supply  seven  tons  of  steam.  The  second-rate  coal  will  give 


128  THE  EAILWAY  LOCOMOTIVE 

eight  tons  for  the  same  money.     Here  then  we  have  one  factor 
in  the  work  of  selecting  coal. 

But  not  only  has  the  cost  of  steam  to  be  considered,  but  the 
rate  at  which  it  is  made.  Thus  a  coal  in  other  ways  desirable 
on  the  score  of  price,  might  be  quite  unfit  for  express  work,  when 
the  power  of  the  engine  is  taxed  to  the  utmost  and  steam  must 
be  made  as  quickly  as  possible.  The  cheaper  coal  might,  however, 
answer  very  well  for  goods  and  slow  passenger  trains.  The  dear 
coal  might  be  a  necessity  for  one  class  of  traffic,  and  cheap  coal 
quite  suitable  to  another. 

In  the  present  day,  moreover,  there  is  a  factor  so  important 
that  it  in  a  way  overshadows  all  others.  The  coal  burned  on 
long  continuous  runs,  such  as  are  now  fairly  common  on  most 
lines,  must  be  free  from  any  impurity  which  will  cause  clinkering. 
Lime  is  a  great  offender  in  this  respect.  Again,  a  trace  of  iron 
will  cause  the  formation  of  "  birds'  nests  " — rings  of  clinkers  like 
india  rubber  umbrella  rings — round  the  ends  of  the  tubes  in  the 
fire-box,  which  obstruct  the  draught.  At  sea  and  on  land,  fires 
can  always  be  cleaned,  but  no  cleaning  can  take  place  with  a 
running  locomotive.  If  clinkers  form  on  the  fire  bars  they  may 
indeed  be  broken  up,  but  the  steaming  power  of  the  boiler  will 
be  seriously  affected.  Time  cannot  be  kept  with  a  "  dirty  fire." 
The  coal  used  on  these  long  runs  is  known  by  experience  to  be 
good.  Nothing  that  can  be  done  in  the  laboratory  can  give  the 
same  certainty  of  the  attainment  of  a  desirable  result. 

Another  quality  essential  to  a  good  locomotive  coal  is  its 
keeping  power.  Large  quantities  are  of  necessity  stored  by  the 
railway  companies.  The  coal  parts  continuously  with  its  more 
volatile  constituents.  No  coal  a  year  old  is  as  good  as  coal 
fresh  from  the  mine.  Some  of  the  Welsh  steam  coals,  in  other 
respects  the  best  coal  in  the  world,  deteriorate  rapidly  by 
"weathering."  Some  of  the  bituminous  coals  will  keep  for 
years  with  little  loss.  It  is  practically  impossible  to  gather  from 
chemical  analysis  whether  a  coal  will  keep  well  or  not ;  experience 
is  the  only  certain  guide.  Yet  another  factor  is  the  mechanical 
structure  of  the  coal.  Thus,  some  coals,  otherwise  excellent,  are 
exceedingly  friable.  They  fall  into  dust  the  moment  they  enter 


FUEL  1JJ9 

the  furnace,  and  go  through  the  bars  or  up  the  chimney.  They 
are  besides  bad  to  handle,  being  brittle  and  producing  a  large 
quantity  of  slack  and  dust  when  put  in  or  taken  out  of  wagons 
or  tenders.  Others  again  swell  up  in  the  fire,  and  check  the 
passage  of  air. 

It  will  be  seen  that  while  the  selection  of  a  coal  is  simplified 
so  long  as  it  is  obtained  from  certain  seams  whose  quality  is 
well  known  and  whose  reputation  is  kept  up,  it  is  by  no  means 
easy  when  new  supplies  are  offered  in  the  half-yearly  competition 
for  railway  coal  contracts. 

We  now  come  into  a  region  of  pure  empiricism,  namely,  the 
process  of  burning  the  coal  whatever  may  be  its  quality.  We 
have  seen  how  much  air  is  needed,  in  theory — what  the  actual 
quantity  used  is  no  one  knows,  because  it  cannot  be  measured. 
The  firing  of  a  locomotive  is  skilled  work.  To  get  the  best 
results  is  an  art  not  to  be  acquired  in  a  few  months,  and  never 
acquired  at  all  by  some  men  ;  and  the  reason  is  that  there  are 
factors  in  operation  which  are  quite  inexplicable  on  any  known 
theory,  and  which  can  only  be  utilised  or  combated  by  men 
who  thoroughly  comprehend  what  they  are  doing. 

It  is  to  be  understood  that  we  are  speaking  now  of  express 
locomotives  hauling  heavy  passenger  trains  at  high  speeds.  As 
a  rule,  the  boilers  of  these  engines  are  worked  very  nearly  to 
their  utmost  capacity.  It  is,  therefore,  inevitable  that  the  fire 
shall  be  kept  in  the  best  possible  condition  for  steam-making. 
What  is  that  condition  ?  It  is  not  unlikely  that  it  is  different 
for  every  engine.  But  leaving  this  on  one  side,  only  a  general 
answer  can  be  given.  It  is  a  matter  of  common  knowledge  with 
all  those  who  have  to  do  with  the  generation  of  high  temperatures 
by  the  direct  firing  of  coal,  that  it  is  possible  to  attain  certain 
conditions  which  result  in  maximum  efficiency ;  and  that  these 
conditions  can  be  quite  easily  upset  by  trifling  changes  apparently 
quite  inadequate  to  the  results  they  bring  about. 

Applying  this  to  a  locomotive,  we  find  that  everything  is  going 
well ;  she  is  keeping  time ;  the  pressure  gauge  is  steady,  and  the 
water  at  the  proper  level ;  suddenly  the  steam  begins  to  fall.  To 
all  intents  and  purposes,  the  fire  is  apparently  as  it  was.  The 

B.L.  K 


130  THE  EAILWAY  LOCOMOTIVE 

mischief  may  have  been  wrought  by  putting  a  couple  of  shovelfuls 
of  coal  too  far  forward  under  the  bridge.  Why  this  should  be  so 
harmful  no  one  knows.  The  mere  levelling  of  the  surface  of 
the  fire  may  have  an  important  effect.  One  day  an  engine  will 
steam  well,  another  day  all  the  efforts  of  the  most  skilful  fireman 
"  will  not  get  her  out  of  the  sulks."  The  locomotive  sets  science 
at  defiance.  Just  as  the  best  powers  of  a  horse  or  a  yacht  are 
only  put  forth  in  obedience  to  the  will  of  someone  who  knows 
just  what  to  do  and  how  to  do  it,  so  does  the  locomotive  depend 
for  its  efficiency  on  the  driver  and  fireman — a  fact  either  not 
known  at  all  to  the  general  public,  or  but  faintly  appreciated. 

Inasmuch  as  the  hauling  power  and  speed  of  a  locomotive 
engine  depend  on  the  quantity  of  steam  that  can  be  made  in  a 
given  time,  a  primary  consideration  is  the  rate  at  which  coal  can 
be  burned.  If,  for  example,  one  engine  can  burn  30  Ibs.  a  minute, 
and  another  engine  60  Ibs.  it  is  clear  that,  other  things  being 
equal,  the  latter  engine  is  twice  as  powerful  as  the  former.  Now 
the  quantity  that  can  be  burned  in  a  given  time  depends  on  the 
amount  of  air  that  can  be  supplied  to  the  furnace.  So  far  no  one 
knows  how  quickly  coal  will  combine  with  oxygen.  When  the  coal 
is  in  the  condition  of  dust  it  will  burn  so  fast  that  it  explodes. 
Awful  catastrophes  have  taken  place  in  coal  mines  because  of 
the  chance  ignition  of  the  dust  which  filled  the  air  in  the  workings.1 
The  weight  of  air  which  enters  the  fire-box  depends  on  the  resis- 
tance to  its  entrance  and  the  force  available  to  overcome  that 
resistance.  This  force  is  supplied  by  the  establishment  of  a 
partial  vacuum  in  the  smoke-box.  Other  things  being  equal,  the 
larger  the  grate  the  less  the  resistance  to  the  passage  of  air. 
The  products  of  combustion  have  to  get  into  the  tubes  and  rush 
through  them.  The  combined  area  of  opening  through  the  tubes 
at  the  fire-box  end  is  called  the  "calorimeter  "  of  the  boiler.  It 
must  not  be  confounded  with  an  instrument,  also  called  a  calori- 
meter, by  which  the  wetness  of  steam  is  measured  and  about 
which  more  will  be  said  presently.  Let  us  suppose  that  a  given 
boiler  has  200  flue  tubes,  each  2  inches  in  diameter  inside.  The 
cross  sectional  area  of  each  is  3*14  inches  and  3*14  X  200  =  628 

1  Dusty  mines  are  carefully  watered  in  the  present  day  as  a  safeguard. 


FUEL  131 

square  inches.  This  is  much  less  than  the  area  through  the 
grate  bars  ;  very  much  less  than  the  area  of  fire  hole  combined 
with  that  of  the  grate  opening.  It  would  be  wrong,  however, 
to  suppose  that  it  is  too  small.  So  far  is  this  from  being  the  case 
that  it  is  only  with  the  greatest  difficulty  that  an  equal  distribu- 
tion of  the  products  of  combustion  among  the  tubes  can  be 
secured.  They  invariably  follow  the  line  of  least  resistance. 
It  may  be  taken  that  in  general  they  will  select  the  highest 
tubes  and  will  avoid  those  at  the  sides,  but  as  will  be  shown 
presently,  there  are  exceptions. 

Draught  is  measured  in  inches  of  water.  The  horizontal 
prolongation  of  one  leg  of  a  U-shaped  glass  tube  passes  through 
the  side  of  the  smoke-box.  When  the  engine  is  running,  the 
exhaust  establishes,  as  we  have  seen,  a  partial  vacuum  in  the 
smoke-box.  The  water  falls  in  one  leg  of  the  vacuum  gauge  and 
rises  in  the  other.  The  difference  in  level  is  measured  in  inches 
and  fractions  of  an  inch.  Under  ordinary  working  conditions  it 
varies  between  about  one  inch  and  seven  inches.  In  1898, 
Mr.  J.  A.  Aspinall  read  a  paper  before  the  Institution  of 
Mechanical  Engineers  recording  draught  experiments  which  he 
had  carried  out.  These  go  to  show,  as  was  to  be  expected,  that  the 
air  pressures  vary  all  through  the  locomotive  boiler.  From  5  up 
to  as  much  as  18  inches  of  vacuum  have  been  measured  in  the 
chimney  ;  3  to  7  inches  in  the  smoke-box  ;  and  1  to  3  inches  just 
over  the  brick  arch.  With  a  vacuum  of  3  inches  in  the  smoke-box, 
60  Ibs.  of  coal  per  square  foot  of  grate  per  hour  were  burned .  There 
seems  to  be  reason  to  suppose  that  the  rate  of  combustion  varies 
directly  in  any  given  engine  as  the  square  root  of  the  air 
gauge  height.  Mr.  Paul  holds  that  applying  this  rule  to  Mr. 
Aspinall's  results,  a  vacuum  of  3  inches  in  the  fire-box  would 
enable  60  X  V3  =  105  Ibs.  per  square  foot  per  hour  to  be 
burned. 

The  weight  of  the  coal  burned  is  always  expressed  in  terms  of 
square  feet  of  total  grate  area  and  hours.  Thus,  let  us  suppose 
that  an  engine  with  17  square  feet  of  grate  is  running  at  30  miles 
an  hour,  and  burning  30  Ibs.  of  coal  per  mile.  As  a  mile  is 
traversed  in  two  minutes,  the  consumption  is  15  Ibs.  per  minute 

K2 


132  THE    EAILWAY  LOCOMOTIVE 

900 

and  900  Ibs.  per  hour.     Then  -^— -  =  53  Ibs.  nearly.     The  con- 
sumption is  53  Ibs.  per  square  foot  of  grate  per  hour. 

Nominally  coal  can  be  burned  at  nearly  three  times  this  rate 
by  the  aid  of  fans ;  but  a  considerable  quantity  then  goes  out  of 
the  chimney  in  the  shape  of  cinders  and  large  sparks.  If  we 
look  into  a  locomotive  boiler  furnace  through  blue  glass  to  save 
our  eyes  from  the  blinding  glare,  it  will  be  seen  that  the  surface 
of  the  fire  is  covered  with  dancing  incandescent  fountains  of  fine 
coal  carried  up  by  the  force  of  the  inrush  of  air  through  the  fire- 
bars. If  the  draught  is  strong  enough  cinders  may  be  seen  snatched 
up  and  thrown  over  the  bridge  to  enter  the  tubes.  One  hundred 
pounds  of  coal  appears  to  be  the  maximum  that  can  be  burned 
without  much  waste  per  square  foot  per  hour.  These  high  rates 
of  combustion  are  accompanied  by  extremely  high  temperatures. 
It  is  quite  possible  that  as  much  as  3,000°  F.  may  be  reached 
in  the  heart  of  the  fire  with  good  coal,  and  2,500°  F.  anywhere 
in  the  fire-box.  When  cast-iron  fire  bars  were  used,  it  was  not 
at  all  an  uncommon  event  to  melt  half  a  dozen  down,  and  bring 
a  run  to  an  abrupt  conclusion.  The  risk  is  diminished  in  the 
present  day  by  using  wrought  iron  or  steel  fire-bars,  which  are 
very  infusible.  Excellent  fire  bricks  are  required  for  the  arch, 
which  is  severely  tried,  not  only  by  the  extreme  heat  but  by 
the  jolting  of  the  engine.  One  way  of  expressing  the  power  of  a 
boiler  is  in  terms  of  pounds  of  water  evaporated  per  hour  per 
square  foot  of  grate  surface ;  thus,  if  the  53  Ibs.  of  coal  spoken 
of  above  made  370  Ibs.  of  steam,  then  it  would  be  said  that  the 
boiler  was  capable  of  evaporating  370  Ibs.  of  water  per  hour  per 
square  foot  of  grate. 

The  next  factor  is  the  heating  surface,  that  is  to  say,  all  the 
inside  of  the  fire-box  and  of  the  tubes.  If  there  are  60  square 
feet  of  heating  surface  to  one  of  grate,  then  the  evaporation 

370 
would  be  -T^T-  =  6*16  Ibs.  of  water  per  square  foot  of  heating 

surface.     These  figures  are  given  simply  for  the  sake  of  illustra- 
tion.    What  the  real  figures  may  be  will  be  set  forth  presently. 
Aa  the  hot  products  of  combustion  pass  through  the  tubes 


FUEL  133 

they  are  cooled  down.  Entering  the  tubes  at,  say,  2,000°  F. 
they  leave  them  at,  say,  700°  F.  The  greater  the  difference  in 
temperature  between  the  gas  and  the  water  in  the  boiler  the 
more  rapid  will  be  the  loss  of  heat  by  the  gas.  It  follows,  there- 
fore, that  the  heating  surface  of  the  tubes  is  more  effective  near 
the  fire-box  than  it  is  near  the  smoke-box.  It  has  been  said,  with 
a  fair  approximation  to  the  truth,  that  one-half  of  all  the  steam 
made  in  a  locomotive  boiler  is  produced  by  the  fire-box  and  the 
first  three  inches  of  the  tubes. 

To  ascertain  facts,  the  engineers  of  the  Chemin  de  fer  du  Nord 
carried  out  a  series  of  experiments  which  have  long  been  regarded 
as  classical.  These  experiments  have  been  recorded  by  MM. 
M.  C.  Cotiche  and  Paul  Havrez  in  1875  and  1876.  The  boiler  of 
a  small  locomotive  was  divided  by  thin  plate  iron  partitions 
into  four  sections.  The  first  plate  next  the  fire-box  was  only 
3J  inches  from  the  tube  plates.  The  fire-box  was  3  feet  square, 
with  9  square  feet  of  grate  and  a  heating  surface  of  60'28  square 
feet ;  the  tubes  were  125  in  number,  12  feet  4  inches  long,  and 
about  If  inches  diameter.  The  boiler  barrel  was  divided  into  four 
sections,  each  3  feet  and  a  fraction  long.  Each  section  could  be 
tried  separately  under  steam  of  the  ordinary  working  pressure. 
The  draught  was  got  by  steam  from  another  boiler.  The 
conditions  of  the  trial  could  be  varied  by  plugging  the  tubes. 
The  total  heating  surface  with  the  tubes  all  open  was  792*43  square 
feat ;  with  one-half  plugged,  424  square  feet. 

The  result  of  this  series  of  trials  showed  that  from  two-fifths  to 
one-half  of  the  whole  quantity  of  water  was  evaporated  in  the 
fire-box  section,  which  was  about  one-tenth  of  the  whole  surface. 
The  table  on  page  134  gives  some  of  the  principal  results,  the 
fuel  being  (1)  coke  and  (2)  briquettes. 

These  figures  are  very  instructive.  They  show  that  the 
efficiency  of  the  tubes  depends  very  much  on  the  weight  of  hot 
gas  passing  through  them,  and  on  the  nature  of  the  fuel  burned. 
It  will  be  seen  that  in  all  cases  the  briquettes  gave  the  best 
results ;  and  this  particularly  when  the  consumption  was  least. 
The  explanation  of  this  is  worth  stating,  because  the  fact  is  not 
without  its  influence  on  locomotive  boiler  design. 


134 


THE  KAIL  WAY  LOCOMOTIYE 


It  has  been  incidentally  mentioned  above  that  at  one  time  it 
was  believed  that  flame  would  not  pass  through  a  small  tube. 
In  treatises  on  smoke  prevention  one  still  finds  an  analogy 
established  between  the  safety  lamp  and  a  locomotive  boiler. 
The  safety  lamp  may  become  filled  with  gas  flame,  the  gas — fire 
damp — passing  through  the  gauze  ;  but  the  flame  will  not  explode 
the  mixture  in  the  mine  because  flame  cannot  pass  through 


Weight  of  fuel  burned 
per  foot  of  grate  per 
hour. 

Quantity  of  water  evaporated  per  hour  per  60  degrees  to  steam  at 
60  Ibs.  pressure. 

1st  section. 

2nd  section. 

3rd  section. 

4th  section. 

5th  section. 

COKE  : 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

48-5  Ibs. 

20 

0-6 

2-9 

1-28 

•72 

85-7    ,, 

23-6 

10-6 

5-8 

3-44 

2-47 

BRIQUETTES  : 

53  Ibs. 

23-5 

5-4 

2-o 

1-33 

•83 

109   ,, 

38-9 

14 

6-8 

4-32 

2-81 

BRIQUETTES  : 

WITH  HALF  THE  TUBES  PLUGGED. 

Ibs. 

Ibs. 

Ibs.               Ibs.               Ibs. 

43    Ibs. 

26  o 

9 

4                 2-1                1-31 

94-3  „ 

44-7 

21 

10-6              6-34 

4-76 

small  orifices  and  so  cannot  get  out  of  the  lamp.  This  is,  how- 
ever, only  one  of  those  half-truths  whose  propagation  has  done 
so  much  harm  in  the  world.  It  is  only  true  of  the  lamp  if  it  is 
shielded  from  a  strong  current  of  air ;  otherwise  the  flame  will 
be  forced  through  the  gauze  with  perfectly  appalling  results. 
Whether  flame  will  or  will  not  pass  through  the  flue  tubes  of  a 
locomotive  depends  in  like  manner  altogether  on  the  draught  and 
on  the  diameter  of  the  tubes.  A  moderate  vacuum  in  the  smoke- 
box  will  pull  flame  for  as  much  as  6  feet  through  a  2J-inch  tube. 


FUEL  135 

In  a  locomotive  worked  to  its  maximum  power  there  is  little 
doubt  that  flame  may  extend  a  long  way  even  in  a  2-inch  tube. 
If  it  did  not  then  it  would  be  mere  waste  of  material  to  use,  as 
is  done  abroad,  tubes  as  much  as  14  to  20  feet  long  with  bitumi- 
nous coal.  The  tubes  in  M.  Couche's  boiler  were  12  feet 
4  inches  long.  It  will  be  seen  that  the  last  3  feet  or  so  added  so 
little  to  the  total  result  that  it  might  have  been  suppressed,  at  all 
events  with  coke  as  a  fuel,  with  apparently  small  loss.  The 
reduced  cost  of  the  boiler  and  its  diminished  weight  would 
probably  have  gone  far  in  the  way  of  compensation.  It  will 
be  noticed  that  the  briquettes  were  under  all  conditions  better 
than  the  coke.  Now  there  were  no  special  smoke  prevention 
appliances,  and  briquettes  usually  make  much  smoke.  The 
probability  is  that  the  tubes  were  filled  for  a  portion  of  their 
length  with  red-hot  flame.  The  flame  from  a  coke  fire  (if  any) 
is  blue,  and  of  the  Bunsen  burner  character.  But  the  Bunsen 
flame  gives  out  little  or  no  radiant  heat.  The  late  Sir  William 
Anderson  years  ago  called  attention  to  the  circumstance  that 
smoke  prevention  appliances  to  steam  boilers,  while  often  success- 
ful in  one  way,  failed  in  another.  A  dull  smoky  flame  filling 
flues  radiates  heat  with  great  power,  which  clear  flame  does  not ; 
and  the  result  was  that  while  the  economy  of  a  boiler  might 
perhaps  be  increased,  its  steam-making  power  was  diminished. 
In  the  United  States,  tubes  as  much  as  3  inches  in  diameter  and 
of  great  length  are  used  in  the  mammoth  engines  of  which  so 
much  is  heard.  It  is  fairly  certain  that  only  the  presence  of 
flame  in  them  renders  the  great  length  of  them  economical. 


CHAPTEE   XVII 

THE    FRONT    END 

WE  have  now  to  consider  the  results  obtained  in  everyday 
practice,  and  this  cannot  better  be  done  than  by  reference  to 
direct  experiment. 

Perhaps  the  most  complete  experiments  of  the  kind  ever 
carried  out  were  those  made  by  Professor  Goss,  of  Purdue 
University,  U.S.A.,  with  an  engine  known  as  "  Schenectady 
No.  1,"  a  second  engine  known  as  "  Schenectady  No.  2,"  and  at 
the  St.  Louis  Exhibition. 

With  "  Schenectady  No.  1  " — a  fairly  typical  American  loco- 
motive— as  much  as  181  Ibs.  of  Indiana  block  coal  were  burned 
per  square  foot  of  grate  surface  per  hour  ;  1,037  Ibs.  of  water 
were  evaporated  per  square  foot  of  grate,  and  14*93  Ibs.  per 
square  foot  of  heating  surface  per  hour,  representing  518  i.h.p. 
Taking  a  normal  rate  of  combustion,  namely,  64  Ibs.  per  foot  of 
grate,  the  evaporation  was  507  Ibs.  and  7*20  Ibs.  The  latter  is 
the  more  important  figure,  because  the  power  of  a  locomotive  is 
very  usually  estimated  by  its  heating  surface.  A  normal 
English  locomotive  with  1,500  square,  feet  of  heating  surface 
may  be  counted  upon  to  convert  7  X  1,500  =  10,500  Ibs.,  or 
1,050  gallons  of  water  into  steam  per  hour.  If  the  engine  uses 
30  Ibs.  of  steam  per  effective  horse-power  per  hour,  that  is  to 
say,  at  the  rails,  then  we  have  350  h.p.  available  for  haulage, 
including,  of  course,  the  engine  and  tender.  This  is,  however, 
far  from  representing  the  maximum  effort  of  which  such  an 
engine  would  be  capable.  The  coal  used  by  Professor  Goss  was 
soft  and  of  indifferent  quality.  Judged  by  the  conditions  laid 
down  above,  the  best  result  obtained  was  only  7'67  Ibs.  of  steam 
per  pound  of  coal,  and  that  was  in  only  one  experiment.  The 


THE  FEONT  END  137 

average  was  under  6  Ibs.  With  English  or  Welsh  coal,  8  Ibs.  might 
be  reckoned  upon,  which  could  give  one-third  more  steam,  other 
things  remaining  equal,  and  about  465  horse-power. 

At  the  Louisiana  Exhibition,  the  De  Glehn  compound  engine, 
very  similar  to  "  La  France,"  put  to  work  on  the  Great  Western 
Railway,  evaporated  8*83  Ibs.  of  water  per  square  foot  of  heating 
surface,  the  temperature  of  the  feed  being  taken  as  212°  F., 
and  the  boiler  was  rated  as  680  horse-power,  and  the  total 
heating  surface  2,656  square  feet,  if  the  inside  of  the  tubes  is 
taken,  and  1,646  square  feet  if  the  outside.  The  difference  is 
due  to  the  fact  that  the  boiler  is  fitted  with  Serve  tubes,  so 
called  after  the  inventor,  which  have  eight  longitudinal  ribs 
inside  them. 

We  now  come  to  the  consideration  of  the  leading  end  of  the 
boiler — that  section  of  it  on  which  the  chimney  stands.  It  is  an 
obvious  cylindrical  continuation  of  the  barrel  of  the  boiler,  and 
is  known  as  the  smoke-box.  Until  recently  it  was  short — just 
long  enough  to  accommodate  the  flange  by  which  the  chimney  is 
bolted  to  it ;  but  of  late  what  is  known  as  "  the  extended  smoke- 
box"  has  been  introduced  from  the  United  States.  It  reaches 
out  far  in  front  of  the  chimney.  The  back  plate  of  the  smoke- 
box  is,  as  has  already  been  stated,  the  front  tube  plate.  In  the 
front  of  the  smoke-box  is  a  large  circular  door  made  with  great 
care  and  accurately  fitted,  so  that  when  closed  and  bolted  no  air 
may  leak  in.  The  bolts  are  moved  by  a  central  handle  which  in 
turn  can  be  locked  by  a  second  handle  on  the  same  spindle.  The 
door  is  required  to  give  access  to  the  tubes  so  that  they  may  be 
swept  or  "  run."  The  tool  used  is  a  long  rod  with  an  eye  at  the 
end  through  which  some  oakum  or  a  strip  of  canvas  is  threaded. 
Ashes  which  collect  in  the  smoke-box  are  removed  from  time  to 
time  through  this  door. 

The  smoke-box  is  included  in  what  has  come  to  be  known  as 
"  the  front  end."  It  plays  a  part  not  less  important  than  the 
fire-box  in  the  daily  life  of  the  locomotive  ;  and,  as  has  already 
been  stated,  its  construction  and  action  have  from  an  early  period 
in  railway  history  been  made  the  subject  of  keen  controversy 
and  many  inventions.  The  functions  of  the  smoke-box  cannot, 


138  THE   RAILWAY  LOCOMOTIYE 

perhaps,  be  better  described  than  in  the  following  extract  from 
Professor  Goss's  recent  book  on  "Locomotive  Performance," 
detailing  the  results  of  experiments  carried  out  since  September, 
1891,  at  Purdue  University,  Lafayette, '  Indiana,  U.S.A.  "The 
term  '  front  end '  refers  to  all  that  portion  of  a  locomotive 
boiler  which  is  beyond  the  front  tube  plate.  It  includes  the 
extended  shell  of  the  boiler  which  forms  the  smoke-box,  and  in 
general  all  mechanism  which  is  therein  contained,  such  as  steam 
and  exhaust  pipes,  netting,  diaphragm,  and  draught  pipes.  It 
also  includes  the  stack  [chimney].  The  front  end  as  thus  denned 
is  to  be  regarded  as  an  apparatus  for  doing  work,  receiving 
energy  from  a  source  of  power  and  delivering  a  portion  thereof 
in  the  form  of  a  specific  result.  The  source  of  power  is  the  exhaust 
steam  from  the  cylinders,  and  the  useful  work  accomplished  is 
represented  by  the  volumes  of  furnace  gases  which  are  delivered 
against  the  difference  of  pressure  existing  between  the  smoke- 
box  and  the  atmosphere.  That  the  power  of  the  jet  may  be 
sufficient,  it  is  necessary  that  the  engines  of  the  locomotive 
shall  exhaust  against  back  pressure.  The  presence  of  the  back 
pressure  tends  to  lower  the  cylinder  performance,  and  it  is  for 
this  reason  that  designers  of  front  ends  have  sought  to  secure 
the  required  draught  action  in  return  for  the  least  possible  back 
pressure.  In  other  words,  the  effort  has  been  to  increase  the 
ratio  of  draught  to  back  pressure,  which  ratio  has  been  defined 
as  the  efficiency  of  the  front  end.  The  office  of  the  front  end  is 
to  draw  atmospheric  air  into  the  ash  pan,  thence  through  the 
grate  and  fire ;  to  draw  the  furnace  gases  through  the  tubes 
of  the  boiler ;  thence  under  the  diaphragm  and  into  the  front 
end ;  and  to  force  them  out  into  the  atmosphere.  In  order  that 
this  movement  may  take  place  a  pressure  less  than  that  of  the 
atmosphere  is  maintained  in  the  smoke-box,  so  that  when  the 
locomotive  is  working  there  is  a  constant  flow  from  the  atmo- 
sphere along  the  course  named  and  back  to  the  atmosphere 
again.  The  difference  in  pressure  between  the  atmosphere  and 
the  smoke-box  is  spoken  of  as  the  draught,  and  under  normal 
conditions  of  running  is  represented  by  from  4  inches  to  10 
inches  of  water."  As  a  result  of  a  multitude  of  experiments 


THE  FEONT  END 


139 


carried  out  with  the  locomotive  "  Schenectady  No.  1,"  Professor 
Goss  gives  the  following  table : — 

PERCENTAGE  OF  TOTAL  DRAUGHT  REQUIRED. 


Miles  per  hour. 

To  draw  air  into 
fire-box. 

To  draw  gases  through 
tubes. 

To  draw  gases  under 
diaphragm. 

20 

22-6 

41  -1 

36'3 

30 

30-1 

33-6 

36-3 

40 

30-4 

32-0 

37-6 

All  this  is  excellent  as  far  as  it  goes,  but  it  does  not  go  far 
enough.  It  is  not  throughout  of  general  application,  and  to 
practice  in  this  country  much  does  not  apply  at  all. 

The  diaphragm  is  a  baffle  plate  introduced  to  beat 
down  the  cinders  and  sparks  and  prevent  their  flight  up  the 
chimney.  Diaphragms  find  no  place  in  English  locomotives. 
Again,  as  has  already  been  explained,  a  large  percentage  of  all 
the  air  required  comes  in  through  the  open  fire  door,  which 
offers  little  resistance.  The  major  part  of  the  work  done  by  the 
exhaust  in  an  English  locomotive  is  expended  in  overcoming  the 
friction  of  the  tubes,  and  the  netting  or  other  devices  used  to 
prevent  the  ejection  of  sparks  and  cinders,  and  in  the  lifting  and 
propulsion  of  the  products  of  combustion  up  to  the  top  of  the 
chimney.  The  products  of  combustion  and  the  air  taken  together 
will  represent,  say  20  Ibs.  per  pound  of  coal  burned.  Let  this  be 
40  Ibs.  per  mile,  and  the  speed  a  mile  a  minute,  then  we  shall  have 
800  Ibs.  If  the  engine  is  indicating  500  horse-power,  and  using 
25  Ibs.  of  steam  per  horse-power  per  hour,  we  shall  have  208  Ibs. 
of  steam  to  add,  that  is  to  say,  about  1,000  Ibs.  of  air  and 
steam  to  be  lifted  per  minute  and  blown  out  of  the  chimney  top 
at  a  high  velocity.  Again,  Professor  Goss  worked  with  an 
engine  standing  in  a  shed,  and  consequently  took  no  account  of 
the  effect  which  may  be  produced  by  the  rush  of  air  through  the 
front  of  the  ash  pan,  which  may  easily  amount  to  several  inches 
of  water.  At  sixty  miles  an  hour,  or  88  feet  per  second,  the 
pressure  of  the  air  on  a  flat  surface  is  about  17  Ibs.  per  square 


140 


THE   RAILWAY  LOCOMOTIVE 


foot,  or  about  3  inches  water  pressure  per  square  inch.     This  is 
the  force  of  a  full  gale. 

The  designers  of  smoke-boxes  in  this  country  are  trammelled 
by  legal  restrictions  which  either  do  not  exist  at  all  in  the 
United  States,  or  only  in  a  lesser  degree.  It  will  not  be  far 


FIG.  50. — Smoke-box,  London  and  South  Western  Railway. 

from  the  truth  to  say  that  the  first  consideration  with  the 
designer  here  is  that  the  locomotive  shall  not  be  likely  to  set  fire 
to  fields  of  standing  corn,  stacks,  hay-ricks  or  woods  past  which 
it  runs  ;  the  second  is,  that  the  production  of  black  smoke  may 
be  avoided ;  the  third,  that  the  back  pressure  in  the  cylinders 
may  be  as  small  as  possible,  and  the  fourth,  that  the  distribution 
of  heat  among  the  tubes  shall  be  quite  equal. 


THE   FRONT  END 


141 


FIG.  51. — Smoke-box,  South  Eastern  and  Chatham  Railway. 


142 


THE   EAILWAY  LOCOMOTIVE 


FIG.  52. — Smoke-box,  South  Eastern  and  Chatham  Railway. 


THE   FRONT  END  143 

As  to  the  first  point,  it  has  usually  been  found  sufficient  to 
place  a  flat  grating  in  the  smoke-box  above  the  level  of  the  tubes. 
Against  the  bars  of  the  grating  cinders  strike,  and  are  either 
broken  so  small  that  they  can  do  no  harm  if  they  pass  through, 
or  else  fall  to  the  bottom  of  the  box.     A  second  device  is  the 
invention   of   Mr.  D.  Drummond,   of   the   London   and    South 
Western  Eailway,  which  is  illustrated  on  p.  140,  and  may  be 
thus  described,  Fig.  50.     In  the  smoke-box  are  placed  two  plates 
of  thin  steel  A  A.     Between  these  plates  are  fixed  others  B  B, 
closely  perforated ;  C  C  are  the  two  main  steam  pipes,  E  E  is  an 
ejection  pipe  for  the  vacuum  brake.    The  hot  gases  fill  the  smoke- 
box,  and  only  escape  by  passing  through  the  perforations  in  B  B 
from  the  sides  of  the  smoke-box.    Not  only  is  this  a  most  efficient 
spark  arrester,  but  it  is  found  that  the  effect  of  the  blast  on  the 
fire  is  made  more  uniform,  with  a  resulting  economy  not  only  in 
coal  but  in  fire-boxes.      Some  are  now  running  on  the  South 
Western  Railway  which  have  been  in  use  for  about  nine  years,  in 
very  heavy  traffic.      Figs.  51  and  52  illustrate  Stone's   spark 
arrester,  which  has   been  adopted   by  Mr.  Harry  Wainwright, 
Chief  Mechanical  Engineer  of  the  South  Eastern  and  Chatham 
Railway,  for  all  his  fast  passenger  engines.     The  conditions  on 
these  lines  are  very  exacting  because  the  coal  used  is  at  once  dear 
and  not  very  good,  much  of  it  running  small  and  given  to  making 
sparks.      The    drawing   requires  little   or  no  explanation.      A 
double  cone  is  fitted  to  the  base  of  the  chimney  up  the  centre 
of  which,  carried  on  the  ring  T,  the  exhaust  passes.     The  cone 
is  made  of  a  frame  of  ten  bars,  each  1J  inch  wide  by  J  inch 
thick.     In  the  edges  are  notches,  round  the  cone  in  these  notches 
is  wound  a  continuous  steel  wire  J  inch  thick.     The  notches  are 
spaced  wider  and  wider  apart,  counting  from  the  bottom.    Round 
the  blast  pipe  is  a  brass  ring  as  shown,  in  which  slots  are  cut, 
these  carry  the  suction  action  of  the  blast  well  down  in  the  smoke- 
box.     In  order  to  give  access  to  the  tubes  the  whole  lower  cone 
may  be  turned  round  to  the  right  or  left  on  a  pivot  P  by  taking 
out   a   single   pin   A.      This   spark    arrester    works   very    well. 
Mr.  Wainwright  is  perfectly  satisfied  with  it  after  an  experience 
extending  over  several  years. 


CHAPTEE   XVIII 

THE    BLAST    PIPE 

IT  has  already  been  pointed  out  that  the  products  of  com- 
bustion will  take  the  most  direct  course  they  can  find  to  the 
outer  air.  They  will  follow  the  line  of  least  resistance.  The 
object  of  the  designer  is  therefore  to  make  all  lines  of  resistance 
alike,  and  this  seems  to  be  very  fairly  done  by  the  diaphragm 
plate.  Indeed,  Professor  Goss  tells  us  that  a  most  elaborate  set 
of  experiments  failed  to  detect  any  differences  in  vacuum  in  the 
space  between  it  and  the  tube  sheet.  When  the  diaphragm  is 
omitted,  as  in  this  country,  there  is  good  reason  to  believe  that 
the  central  and  topmost  tubes  pass  more  gas  than  the  outer  and 
lower  tubes.  It  does  not  appear,  however,  that  this  seriously 
militates  against  the  efficiency  of  a  boiler. 

The  method  of  operation  of  the  blast  pipe  has  already  been 
explained  in  general  terms.  A  complete  examination  of  the 
problem  which  it  presents  would  be  out  of  place  in  this  book ; 
but  much  that  is  at  once  interesting  and  ought  to  be  known  by 
those  who  wish  to  understand  the  locomotive  remains  to  be  said. 
The  steam  which  has  done  its  work  in  the  cylinders  is  discharged 
up  the  chimney,  in  some  cases  through  one  pipe,  in  others 
through  two  pipes.  In  any  case  the  pipes  are  two  more  in  name 
than  in  reality.  The  blast  pipe  proper  rests  on  a  box  which 
is  a  portion  of  the  cylinders  and  to  which  it  is  bolted.  It  is 
usually  somewhat  oval  in  cross  section  at  the  bottom,  and  tapers 
slightly  to  the  top  where  the  "nozzle"  is  bolted  on.  This  is 
always  bored  out  truly  cylindrical,  and  is  made  as  large  in 
diameter  as  possible,  that  is  to  say,  between  4  inches  and 
oj  inches.  A  greater  diameter  than  5  inches  is  exceptional. 
The  larger  the  diameter  the  better,  because  the  back  pressure  in 


THE   BLAST  PIPE  145 

the  cylinders,  which  is  so  much  waste,  depends  for  its  amount 
more  on  the  diameter  of  the  blast  nozzle  than  on  any  other 
factor.  The  smaller  the  nozzle,  the  greater  is  the  velocity  with 
which  the  exhaust  steam  issues,  and  the  more  powerful  is  its 
action  in  establishing  a  minus  pressure  in  the  smoke-box. 
Therefore,  when  an  engine  is  found  to  steam  badly,  in  the  last 
resort  a  nozzle  of  less  diameter  than  that  in  use  is  put  on. 
This  augments  the  back  pressure  and  decreases  the  power  of  the 
engine ;  but  the  increase  in  the  quantity  of  coal  that  can  be 
burned  in  a  given  time  more  than  compensates  for  this  loss. 
So  that  an  engine  which  will  not  keep  time  with  a  4J  inch  blast 
nozzle  may  very  well  do  so  with  a  4|  nozzle.  This  is  one 
of  the  many  facts  which  show  how  sensitive  a  machine  the 
locomotive  is.  There  are,  however,  other  factors  besides  diameter 
to  be  considered.  It  is  essential  that  the  nozzle  shall  stand 
absolutely  under  the  centre  of  the  chimney,  so  that  a  vertical 
line  may  be  drawn  through  the  centres  of  both.  Care  must  also 
be  taken  that  the  blast  is  not  projected  against  one  side  of  the 
chimney  more  than  the  other.  In  some  cases,  particularly  with 
outside  cylinders,  the  blast  from  one  cylinder  hits  one  side,  and 
from  the  other  cylinder  the  other  side  of  the  chimney,  although 
there  is  only  a  single  nozzle.  This  means  loss  of  efficiency,  and 
to  avoid  it  a  partition  usually  extends  some  way  up  the  vertical 
portion  of  the  blast  pipe.  Again,  the  height  of  the  nozzle  in 
relation  to  the  tubes  is  of  much  importance.  If  it  is  low  it  will 
usually  be  found  that  the  lower  tubes  have  the  better  draught. 
If  it  is  high,  then  the  upper  tubes.  Then  the  relation  of  the 
blast  nozzle  to  the  base  of  the  chimney  has  to  be  considered. 
Sometimes  raising  the  nozzle  improves  the  draught,  sometimes 
lowering  it  has  that  effect.  Then  the  form  of  the  pipe  has  an 
effect.  Various  blast  pipes  have  been  tried,  such  as  Adams' 
Vortex  pipe,  a  concentric  pipe  with  the  exhaust  from  one  cylinder 
passing  through  the  inner  ring  and  the  exhaust  from  the  other 
cylinder  through  the  outer  ring  and  so  on.  It  may  be  said 
that  on  the  whole  the  advantage  derived  from  these  inventions 
has  been  too  small  to  enable  them  to  supersede  the  plain  pipe  to 
any  extent.  But  advantage  has  been  derived  from  supplements, 
K.L.  L 


146  THE  RAILWAY  LOCOMOTIVE 

so  to  speak,  to  the  blast  pipe.  Thus,  in  smoke-boxes  of  large 
diameter,  "  petticoat  "  pipes  are  sometimes  fitted  with  advantage. 
These  are  intended  to  diffuse  the  "  pull  "  of  the  exhaust  and 
equalise  the  draught  among  the  tubes. 

In  all  cases  a  "  blower  "  is  fitted,  which  usually  takes  the  form 
of  a  ring  round  the  top  of  the  exhaust  pipe,  which  is  perforated 
with  a  number  of  small  holes.  Through  ohese,  by  opening  a 
cock  in  the  cab,  steam  can  be  blown  up  the  chimney  to  create  a 
draught  when  the  engine  is  standing.  The  blower  is  used  when 
getting  up  steam ;  in  stations  to  prevent  smoke ;  and  is  always 
turned  on  just  before  steam  is  shut  off  to  prevent  flames  coming 
out  through  the  fire  door,  by  which  the  men  on  the  footplate 
would  be  burned.  Indeed,  men  have  been  killed  in  this  way. 

Until  a  recent  period,  the  chimney  was  always  a  pipe  of  some 
length,  as  much,  for  example,  as  5  feet,  and  it  was  wholly  outside 
the  smoke-box.  But  of  late  years  huge  engines  have  been  built 
with  boilers  of  great  diameter,  and  the  limits  of  height  in  tunnels 
and  under  bridges  have  reduced  the  apparent  length  of  the 
chimney  until  it  has  been  defined  as  "  a  frill  round  a  hole  in  the 
top  of  the  smoke-box  "  ;  in  such  cases  the  chimney  extends  down 
some  distance  into  the  smoke-box. 

A  curious  fact  is  that  on  the  continent  of  Europe  no  such 
uniformity  of  blast-pipe  practice  exists  as  in  this  country. 
There  are,  perhaps,  fifty  different  kinds  of  pipe  and  arrange- 
ments of  the  smoke-box  in  use,  and  while  it  is  claimed  for  each 
that  it  is  the  best  possible,  all  seem  to  answer  their  purpose 
equally  well.  Thus,  on  the  Austro-Hungarian  State  railways, 
the  blast  nozzle  stands  just  inside  the  base  of  the  chimney,  a 
semi-circular  grating  just  above  the  tubes  acting  as  a  spark 
arrester.  On  the  Eastern  Eailway  of  France,  the  chimney  is 
flared  at  the  base,  the  blast  pipe  is  level  with  the  top  of  the 
smoke-box,  and  is  rectangular  instead  of  circular.  The  "  nozzle  " 
is  fitted  with  two  flaps  or  doors  which  can  be  brought  together  or 
separated  by  a  rod  from  the  footplate,  so  that  the  draught  can 
be  adjusted  to  the  demand  for  steam.  An  express  engine  on  the 
Paris,  Lyons  and  Mediterranean  line  has  been  fitted  with  a  nearly 
similar  adjustable  nozzle,  while  inside  the  chimney  is  placed  a 


THE  BLAST  PIPE  147 

long  second  tube  up  which  the  steam  blower  is  turned.  On  the 
Belgian  State  railways  rectangular  chimneys  are  still  in  use. 
The  list  might  readily  be  extended,  if  it  were  necessary,  which  it 
is  not. 

It  is  impossible  to  look  at  locomotives  with  understanding  and 
not  perceive  that  the  chimneys  vary  remarkably  in  form  and 
dimensions.  The  old  rule  was  that  the  chimney  should  be  the 
same  diameter  as  the  cylinder,  and  as  long  as  possible.  Thus, 
an  engine  with  16-inch  cylinders  had  a  chimney  16  inches  in 
diameter.  Not  that  there  was  any  real  connection  between  these 
proportions.  The  tendency  in  the  present  day  is  to  keep  down 
diameter.  Thus,  while  an  engine  with  1,100  square  feet  of 
heating  surface  may  have  a  17-inch  chimney,  one  with  2,200 
feet  will  have  a  chimney  no  larger,  possibly  indeed  smaller.  It 
might  indeed  be  argued  from  modern  practice  that  no  relation 
existed  between  boiler  power  and  the  dimensions  of  the  chimney. 
There  can,  however,  be  no  doubt  that  some  forms  and  sizes  of 
chimney  are  better  than  others,  but  apparently  the  difference  is 
not  great.  Professor  Goss  carried  out  at  Purdue  University  the 
most  elaborate  set  of  experiments  intended  to  give  data  for 
standardising  dimensions  ever  undertaken.  The  experiments 
were  got  up  at  the  instance  of  the  American  Engineer, 
published  in  New  York ;  and  a  very  strong  committee  of  repre- 
sentative railway  engineers  carried  them  out  with  the  aid  of 
Professor  Goss  on  a  locomotive  known  as  "  Schenectady  No.  2," 
a  more  powerful  engine  than  "  Schenectady  No.  1."  It  would  be 
beyond  the  scope  of  this  book  to  give  more  than  the  result  of  the 
inquiry  as  decided  by  the  committee.  This  may  be  stated  in 
six  equations. 

When  the  exhaust  nozzle  is  on  the  centre  line  of  the  boiler 

d  =  '246  +  (-00123  H)  D.  (1) 

Here  d  is  the  diameter  of  the  chimney  in  inches,  H  its  height 
in  inches,  and  D  the  diameter  of  the  front  end,  that  is  to  say 
the  smoke  box,  in  inches. 

Tapered  stacks  were  tried.  It  was  assumed  that  they  would 
act  somewhat  like  a  "  diverging  nozzle,"  and  prove  more  efficient 
than  straight  tubes.  The  experiments  enabled  the  important 

L2 


148  THE   RAILWAY   LOCOMOTIVE 

conclusion  to  be  drawn  that  a  tapered  stack  of  13 J  inches 
diameter  gives  maximum  results  for  all  heights  between  the 
limits  of  26J  and  56^  inches.  The  diameter  of  the  tapered  stack 
does  not  need  to  be  varied  with  change  in  height.  Hence,  we 
may  write  for  all  locomotives  and  all  heights  of  stack  where  the 
exhaust  nozzle  is  on  the  centre  line  of  the  boiler 

d  =  -25  D.  (2) 

Here  d  is  the  least  diameter  of  the  tapered  stack  and  D  the 
diameter  of  the  front  end  of  the  boiler. 

It  must  be  kept  in  mind  that  the  foregoing  equations  only 
apply  when  the  nozzle  is  on  the  centre  line  of  the  smoke-box.  In 
this  country  it  is  almost  invariably  higher,  that  is,  nearer  the  root 
of  the  chimney.  Nor  is  practice  in  the  United  States,  much  less 
in  Europe,  invariable  as  to  the  position  of  the  exhaust  nozzle. 
Therefore,  the  committee  carried  out  further  experiments  with 
varying  heights  of  nozzle,  from  the  results  of  which  Professor 
Goss  prepared  the  following  general  equations  : — 
For  straight  stacks  : 

When   the   exhaust   nozzle   is    below  the  centre  line  of  the 
boiler 

d  =  (-246  +  -00123  H)  D  +  -19/i.  (3) 

When   the   exhaust   nozzle  is  above  the  centre  line  of    the 
boiler 

d  =  ('246  +  '00123  H)  D  -  197*.  (4) 

For  tapered  stacks  : 

When  the  nozzle  is  below  the  centre  of  the  boiler 

d  =  '25  D  +  -16ft.  (5) 

When  the  nozzle  is  above  the  centre  line  of  the  boiler 

d  =  -25  D  -  -16//,  (6) 

Here  d  is  for  (3)  (4)  the  diameter  of  the  stack  in  inches.  For  (5) 
(6)  it  is  the  diameter  of  the  "  choke  "  or  smaller  part :  H  is  the 
height  in  inches  which  should  be  the  greatest  possible  ;  D  is  the 
diameter  of  the  smoke-box  in  inches,  and  h  the  distance  between 
the  centre  line  of  the  boiler  and  the  top  of  the  exhaust  pipe. 
These  particulars  by  no  means  cover  the  whole  ground  traversed 
by  the  committee,  but  they  are  quite  sufficient  for  the 
purpose  of  this  volume.  The  inquiry  appears  to  supply  the 


THE  BLAST  PIPE 


149 


latest  available  information.  As  has  already  been  pointed  out, 
so  much  variation  in  practice  occurs  that  it  is  doubtful  that  it 
has  been  altered  to  any  considerable  extent.  As  a  result  of  the 
investigations,  Professor  Goss  suggests  a  standard  front  end, 
the  general  arrangement  of  which  and  the  chimney  are 
given  in  Fig.  53.  Here  T  is  the  front  tube  plate  and  K  a 
diaphragm,  the  object  of  which  is  to  beat  down  the  cinders 
and  sparks  issuing  from  the  ends  of  the  tubes ;  W  is  the  blast 
nozzle.  The  diaphragm  finds  no  place  in  English  locomotives. 
In  America  it  appears  in  various  forms,  sometimes  as  a  thin  plate 
of  iron,  at  others  as  a  stout  wire  netting.  It  is  invariably  so  made 
that  it  can  easily  be  removed  in  order 
that  the  tubes  may  be  swept.  It  may 
be  taken  as  proved  that  the  diaphragm 
checks  the  draught  about  as  much  as 
the  fuel  on  the  grate,  but  it  appears  to 
be  a  very  efficient  spark  arrester. 

Professor  Goss  gives  the  following 
rules  as  applicable  to  the  standard  front 
end:  — 

Make  H  and  h  as  great  as  possible. 

„      d  =  -21  D  +  -16/i. 

„       b  =   2  d  02  -5  D. 

„      P  =  '32  D. 

„      p  =  -22  D. 

Figs.  54  and  55  are  longitudinal  and  cross  sections  of  the  front 
end  of  a  4 — 4 — 2  Bald  win  compound  "Atlantic  "of  great  size  shown 
at  the  St.  Louis  Exhibition.  The  grate  surface  is  49'5  square 
feet,  the  external  heating  surface  of  the  tubes  is  3016  square  feet, 
that  of  the  fire-box  190  square  feet,  and  the  boiler  pressure  is 
220  Ibs.  There  are  273  tubes  2J  inches  diameter  and  18  feet  9 
inches  long.  The  chimney  for  this  enormous  boiler  is  only  15  f 
inches  diameter  at  the  smallest  part,  which  is  just  f  inch  larger 
than  the  high  pressure  cylinder.  There  are  four  cylinders,  two 
15  inches  and  two  25  inches  diameter,  with  a  stroke  of  26 
inches.  By  the  old  rules  the  chimney  would  have  been  25  inches 
diameter. 


FIG.  53. — Standard  front 
end. 


150 


THE  RAILWAY  LOCOMOTIVE 


THE  BLAST  PIPE  151 

The  diaphragm  next  the  tube  plate  is  of  thin  iron  plate,  the 
remainder  of  it  of  stout  wire  netting  as  shown  in  Fig.  55.  The 
gases  have  to  go  to  the  front  of  the  smoke-box  before  they  can 
reach  the  chimney. 

A  few  words  remain  to  be  said  as  to  the  theory  of  the  blast 
pipe.  It  has  already  been  explained  that  the  friction  of  the 
exhaust  steam  drags  the  products  of  combustion  with  it,  and  that, 
furthermore,  they  find  their  way  into  it  and  mingle  with  it.  This 
they  do  because  the  jet  not  only  exerts  no  lateral  pressure,  having 
no  tendency  to  expand  in  the  ordinary  sense  of  the  term,  but 
because  its  pressure  is  actually  less  than  that  of  the  vacuum  in 
the  smoke-box,  in  the  same  way  and  for  the  same  cause  that  the 
pressure  of  a  fan-blast  is  always  least  at  the  point  in  the  wind- 
trunk  nearest  the  fan  case. 

But  there  is  reason  to  believe  that  another  factor  also  plays  a 
part,  which  has  been  overlooked.  If  left  to  itself,  the  external 
atmosphere  would  rush  down  the  chimney  into  the  smoke-box  to 
fill  up  the  vacuum.  Now  just  at  the  extreme  top  of  the  chimney 
the  blast  acts  to  push  the  air  away.  Its  influence  extends  indeed 
for  some  distance  above  the  stack  to  form  a  second  vacuum  outside 
the  smoke-box,  into  which  the  gases,  of  course,  rush.  Experiments 
carried  out  by  Mr.  Aspinall  go  to  show  that  at  the  very  top  of  the 
stack  a  negative  pressure  equal  to  as  much  as  10  inches  of  water 
may  exist. 

The  reader  has  now  had  placed  before  him  in  a  succinct  form 
sufficient  information  to  enable  him  to  form  a  fairly  complete 
idea  of  the  way  in  which  coal  is  burned  in  a  locomotive.  He  will 
have  seen  that  simple  things  as  the  putting  of  coal  through  a 
fire  hole  and  the  issue  of  heated  gases,  steam,  and,  perhaps, 
smoke  from  the  engine  chimney  may  appear  to  be,  they  are 
really  only  the  initial  and  terminal  stages  of  a  series  of  complex 
processes  on  the  complete  working  out  of  which  depend  the 
success  of  the  locomotive  engine.  While  the  general  reader  may 
rest  content  with  what  he  has  learned  in. this  connection,  it  is 
hoped  that  the  student  will  only  find  that  his  appetite  for  further 
information  has  been  stimulated. 


CHAPTEE  XIX 


STEAM 

WE  have  now  seen  what  goes  on  at  the  fire-side  of  the  heating 
surface.  We  have  next  to  consider  what  takes  place  at  the  water 
side.  Before  going  further,  it  will  be  well  to  give  a  short  state- 
ment of  the  pressures  and  temperatures,  &c.,  most  commonly  met 
with  in  locomotives.  The  reader  will,  perhaps,  scarcely  need  to 
be  told  that  the  temperature  at  which  water  boils  bears,  so  long 
as  the  water  is  pure,  an  unalterable  relation  to  the  pressure.  In 
the  accompanying  table  fractions  have  as  far  as  possible  been 

PROPERTIES  OF  SATURATED  STEAM. 


Boiler 
Pressure. 

Tempera- 
ture. 
Degrees 
Fah. 

Total  Heat 
from  Water  at 
32°. 

Latent 
Heat. 

Weight  of  one 
Cubic  Foot. 

Volume  1  Ib. 
of  steam. 
Cubic  Feet. 

Cubic  Feet 
of  Steam  to 
One  of  Water. 

Ibs. 

Ibs. 

150 

366° 

1193° 

856° 

•3695 

2-71 

169 

160 

371° 

1194° 

853° 

•3899 

2-56 

159 

170 

375° 

1196° 

849° 

•4117 

2-43 

151 

180 

380° 

1197° 

847° 

•4327 

2-31 

144 

188 

382° 

1198° 

845° 

•4431 

2-26 

141 

195 

386° 

1199° 

842° 

•4634 

2-16 

135 

205 

390° 

1200° 

839° 

•4842 

2-06 

129 

215 

394° 

1202° 

836° 

•5052 

1-98 

123 

225 

398° 

1203° 

834° 

•5248 

1-90 

119 

STEAM  153 

omitted,  and  the  nearest  round  numbers  used.  The  figures  refer 
to  what  is  known  as  dry  saturated  steam,  that  is  to  say,  to  steam 
free  from  water  carried  in  the  form  of  spray  or  priming.  The 
pressures  given  are  those  which  are  read  on  steam  pressure 
gauges,  and  are  not  the  absolute  pressures,  which  are  14*73  Ibs. 
higher. 

The  heat  produced  by  the  combustion  of  the  coal  in  the  fire- 
box has  to  be  transferred  to  the  water  in  the  boiler,  and  to  do 
this  it  must  pass  through  the  metal  of  the  plates  and  tubes. 
Precisely  how  the  transmission  takes  place  is  not  known.  In 
effect,  the  side  of  the  plate  next  the  fire  is  made  hotter  than  the 
side  of  the  plate  next  the  water,  and  heat  goes 
through  ;  the  water  side  of  the  plate  being  in 
turn  hotter  than  the  water,  the  transmission  con- 
tinues. This  is  all  apparently  very  simple,  but 
the  process  is  really  complex. 

It  is  assumed  that  the  plate  resists  the  trans- 
mission of  heat  through  its  substance,  and  that 
the  fact  that  one  material  is  a  better  conductor 
of  heat  than  another  is  due  to  variation  in  the 
amount  of  the  resistance.  Hence,  we  find  it 
argued  that  copper  plates  being  much  better 
conductors  of  heat  than  iron  or  steel,  they  are  preferred  by  astute 
railway  engineers  to  steel  or  iron  plates.  There  is,  however,  no 
basis  of  truth  in  this  theory.  Steel  fire-boxes  are  almost  always 
used  in  the  United  States.  They  have  been  tried  in  this  country. 
Careful  experiments,  and  indeed  long-continued  practical  trials, 
show  that  copper  possesses  no  advantage  whatever  over  iron  or 
steel.  It  is  used  because  it  is  much  more  durable  than  any  other 
material ;  and  when  a  copper  fire-box  is  worn  out  it  can  be  sold 
as  old  metal  at  from  50/.  to  701.  a  ton,  according  to  the  state  of 
the  market,  while  an  old  steel  fire-box  will  hardly  pay  the  cost  of 
breaking  it  up. 

The  efficiency  of  a  fire-box  plate  does  not  in  practice  depend  on 

its  conducting  powers  at  all.     It  does  depend  on  its  receiving  and 

emitting  powers.      It  has  been  shown  by  Peclet  and  others  that 

~a  square  inch  of  copper  in  a  fire-box  can  "  conduct  "  about  twelve 


154  THE  EAILWAY  LOCOMOTIVE 

times  as  much  as  it  can  absorb  or  emit.  Thus,  let  A  in  Fig.  56 
be  the  side  of  a  fire-box,  in  which  is  fixed  a  pin  6J  inches  long 
and  1  inch  in  diameter.  A  length  B  of  3  inches  of  the  pin 
is  in  the  furnace  and  a  similar  length  C  in  the  water,  and  it  is  a 
little  over  1J  inch  in  diameter.  Its  cross-sectional  area  at  D  is 
therefore  1  square  inch.  The  surface  which  it  offers  to  the  fire 
is  11*6  inches,  and  that  to  the  water  the  same.  Now,  it  is 
impossible  to  melt  the  3  inches  of  pin  in  the  fire,  simply 
because  all  the  heat  that  the  11/6  inches  of  surface  can  absorb 
can  be  conducted  through  the  square  inch  section  of  pin  in  the 
plate,  and  the  water  will  take  up  the  heat,  provided  the  pin  is 
clean,  and  so  the  pin  is  kept  cool. 

A  knowledge  of  this  fact  led  Mr.  Charles  Wye  Williams,  a  very 
eminent  engineer  in  the  early  portion  of  the  last  century,  to  put 
"heat  pegs"  in  the  furnace  plates  of  boilers.  He  thus  very 
largely  augmented  their  power  ;  but  the  invention  was  doomed 
to  failure  because  it  was  impossible  to  keep  the  pegs  clean  and 
free  from  deposit  on  the  water  side,  and  so  plates  and  pegs  were 
involved  in  one  common  ruin. 

We  may  rest  content,  then-,  that  the  transmission  of  beat  has 
in  practice  nothing  to  do  with  the  conducting  powers  of  the  plate, 
while  it  has  everything  to  do  with  its  emissive  and  absorbing 
powers.  Now  these  depend  on  two  factors.  The  first  is  the  way 
in  which  the  heat  is  applied  to  the  plate ;  the  second  is  the  com- 
pleteness, or  the  reverse,  of  the  contact  of  the  water  with  the 
plate. 

It  may  be  stated  without  fear  of  contradiction  that  the  best 
results  will  be  got  when  the  flame  or  hot  air  impinge  directly  on 
the  plate  to  be  heated,  that  is  to  say,  the  flow  of  the  products  of 
combustion  ought  to  be  at  right  angles  to  the  surface.  The 
impingement  of  the  flame  leads,  furthermore,  to  a  breaking  up 
and  mixing  of  columns  or  bodies  of  hot  gas.  The  parallel  flow 
of  hot  air  or  even  flame  along  a  surface  to  be  heated  is  not  so 
effective.  This  is  no  doubt  one  reason  why  a  tube  ]51ate  does  so 
much  work,  the  products  of  combustion  strike  it  directly  when 
rushing  to  the  tubes. 

All  this  holds  good  to  a  still  greater  extent  as  regards  water, 


STEAM  155 

Water  is  to  all  intents  and  purposes  a  non-conductor  of  heat. 
Any  quantity  of  it  can  only  be  heated  throughout  by  convection, 
that  is  to  say,  only  the  film  in  immediate  contact  with  a  hot  plate 
is  heated.  Fortunately,  water  expands,  and  the  hotter  water 
being  lighter  than  the  cold  rises,  and  is  replaced  by  cold  water, 
which  is  in  its  turn  heated.  This  process  is  termed  convection. 
It  may  be  taken  as  certain,  that  unless  every  drop  of  water  in  a 
boiler  comes  into  contact  either  with  the  heating  surface  or  with 
steam,  it  will  remain  cold.  Water,  it  is  well  known,  cannot  be 
raised  in  temperature  from  above  downwards.  In  marine  boilers 
the  heat  is  always  supplied  at  a  height  of  at  least  3  feet  above 
the  bottom  of  the  boiler.  The  result  is  that  steam  may  be  up 
and  the  engines  at  work  for  an  hour  or  two  while  the  water  at 
the  bottom  of  the  boiler  is  quite  cold.  This  stresses  the  boiler 
plates  severely,  as  the  plates  in  the  steam  space  are  expanded  by 
the  heat,  while  the  bottom  plates  are  not.  The  rolling  and 
pitching  of  the  ship  at  sea  sets  the  water  in  motion,  and  so 
equalises  temperature.  But  it  is  the  custom  nowadays  to  use 
what  is  known  as  a  "  hydrokineter,"  which  is  simply  a  jet  nozzle 
near  the  bottom  of  the  boiler.  A  pipe  from  the  steam  space 
leads  down  to  this,  and  as  soon  as  steam  is  up  to  ten  or  twelve 
pounds  pressure  it  is  sent  through  the  jet  into  the  cold  water, 
where  it  condenses  and  heats  up  the  stagnant  water,  putting  it 
in  motion  at  the  same  time.  In  large  vessels,  as  steam  is  always 
up  in  some  one  boiler  to  supply  electric  light,  &c.,  steam  of  full 
pressure  is  taken  from  this  and  blown  into  the  bottoms  of  the 
other  boilers  as  soon  as  the  fires  are  lighted.  In  the  locomotive 
it  is  true  that  there  is  no  stagnant  water ;  none  the  less  does  the 
incapacity  of  water  to  conduct  heat  play  a  very  important  part, 
as  will  be  understood  in  a  moment. 

Keference  has  been  made  to  Mr.  Charles  Wye  Williams,  who, 
it  may  be  added  incidentally,  was  one  of  the  first  to  make  Atlantic 
steam  navigation  a  success.  He  was  a  most  competent  authority 
on  boiler  furnaces  and  the  prevention  of  smoke.  In  the  year 
1860  he  published  a  very  curious  book,  in  which  he  set  forth  the 
theory  that  water  can  never  be  heated  at  all.  The  application  of 
heat  at  once  transforms  it  into  steam,  and  this  steam  is  diffused 


156  THE  KAILWAY  LOCOMOTIVE 

through  the  main  body  of  the  water,  just  as  carbonic  acid  gas  is 
in  a  bottle  of  "  soda  water."  A  thermometer  put  into  the  water 
is  heated  by  the  steam  in  it.  It  may  be  said  of  this  theory  that 
it  is  very  difficult  to  disprove  it — a  difficulty  augmented  by  the 
circumstance,  already  pointed  out  in  a  preceding  chapter,  that  no 
one  knows  anything  with  any  completeness  of  knowledge  as  to 
how  water  is  converted  into  steam,  or  the  true  difference  between 
dry  saturated  steam  and  water. 

It  will  be  seen  from  what  has  been  said  that  a  steam  boiler 
cannot  be  worked  without  circulation.  Thus  we  find  that  the 
claims  of  various  inventors  of  boilers  always  include  a  statement 
that  the  "circulation  is  excellent,"  or  "the  best  possible,"  or 
"  violent."  In  point  of  fact,  circulation  is  really  a  curse  instead  of 
a  blessing,  but  it  cannot  be  done  without.  In  the  locomotive 
boiler  good  circulation  is  essential  not  only  to  success,  but  to 
safety.  The  heating  surface  must  be  kept  wet,  that  is  to  say,  the 
water  must  be  in  direct  contact  with  it  at  all  times.  If  the 
crown  sheet  of  the  fire-box  of  a  locomotive,  with  a  heavy  fire  on, 
became  dry,  about  thirty  seconds  would  suffice  to  make  it  red  hot, 
when  it  would  be  so  weakened  that  it  would  collapse,  with  the 
most  disastrous  results. 

Now,  so  long  as  the  boiler  is  kept  sufficiently  full  there  will  be 
two  or  three  inches  of  water  over  the  crown  sheet,  and  as  there  is 
free  access  to  it  from  the  boiler  barrel,  and  the  steam  generated 
can  rise  straight  from  it,  we  seldom  hear,  if  the  water  is  good,  of 
the  failure  of  this  plate.  But  the  case  is  entirely  different  with 
the  "  water  legs,"  that  is,  the  space  round  the  bottom  of  the  fire- 
box, and  with  the  tube  sheet.  It  has  already  been  explained  that 
at  the  sides  of  the  fire-box  the  space  filled  with  water  is  some- 
times only  2J  inches  wide,  seldom  more  than  3J  inches.  This  is 
the  portion  of  the  fire-box  in  direct  contact  with  the  burning 
fuel.  The  ebullition  in  these  narrow  water  spaces  must  be  very 
violent,  the  access  of  water  to  them  not  easy.  They  are  in 
point  of  fact  full  of  a  mixture  of  steam  and  water  in  the  condition 
of  foam  rather  than  of  solid  water.  The  plates  are  no  doubt  in 
a  constant  condition  of  over-heat,  and  it  is  not  surprising  that 
cracking  and  buckling  and  deformation  of  the  plates  between  the 


STEAM  157 

stay  bolts  should  be  rife.  Water  legs  should  never  be  less  than 
4  inches  wide.  The  attempt  to  make  the  grate  a  little  wider  by 
narrowing  the  water  legs  is  a  mistake. 

As  to  what  really  takes  place  in  the  water-legs,  some  direct 
information  exists.  In  the  course  of  a  paper  on  "Large  Loco- 
motive Boilers,"  read  by  Mr.  G.  T.  Churchward,  Chief  Mecha- 
nical Engineer  of  the  Great  "Western  Eailway,  he  said  that, 
"  with  modern  high  pressures,  the  rate  of  evaporation  is  so  much 
increased  that  the  provision  for  circulation  which  was  sufficient 
for  the  lower  pressures  formerly  used,  is  doubtless  insufficient." 
The  general  theory  is,  that  cold  water  being  put  into  the  barrel 
near  the  front  end,  sinks  to  the  bottom  under  the  tubes,  and 
flows  back,  entering  the  "  water-legs,"  and  passing  round  the 
back  of  the  fire-box  where  it  rises  and  flows  over  the  top  of  the 
box  forward.  Mr.  Church  ward's  experiments  showed  that  in  the 
main  this  view  was  accurate,  but  a  little  alteration  in  the  firing 
has  the  effect  of  changing  the  direction  of  the  currents  and  even 
of  reversing  them.  This  is  a  fact  of  much  greater  importance 
than  appears  at  first  sight.  It  is  one  explanation  of  the  extra- 
ordinary way  in  which  a  small  mistake  in  firing  may  cause  loss 
of  pressure  in  a  hard-pushed  boiler. 

The  tubes  are  spaced  at  distances  varying  between  f  inch  and 
f  inch,  according  to  the  views  of  the  designers.  When  it  is 
considered  that  the  temperature  at  the  tube  plate  is  probably 
the  highest  in  the  fire-box,  it  is  easy  to  understand  that  here 
again  we  have  a  place  in  which  it  is  impossible  for  "solid" 
water  to  exist.  It  is  in  this  way  that  the  constant  liability  of 
tubes  to  leak  can  be  explained.  It  may,  then,  be  accepted  as 
a  deplorable  fact  that  until  wre  get  to  a  point  a  couple  of  feet 
forward  in  the  barrel,  nothing  but  a  mixture  of  steam  and 
water  is  available  to  keep  the  plates  from  being  overheated. 
The  condition  has  to  be  accepted  ;  but  it  is  responsible  for  rapid 
wear  and  tear,  which  add  largely  to  the  cost  of  maintaining 
locomotives  in  good  order. 


CHAPTER  XX 

WATER 

So  far  all  water  has  been  spoken  of  as  though  it  was  invari- 
ably equally  good  and  suitable  for  a  locomotive  boiler.  But  not 
only  is  this  not  the  case,  but  water  which  will  answer  very  well 
with  pressures  of  150  Ibs.  may  be  quite  unfit  for  boilers  carrying 
200  Ibs.  It  is  almost  impossible  to  command  a  supply  of  pure 
soft  water  all  over  a  great  railway  system.  Nearly  all  the  water 
available  is  more  or  less  "  hard,"  that  is  to  say,  it  carries  salts 
of  lime,  or  magnesia,  or  both  in  solution.  Now  unfortunately 
these  salts  are  more  soluble  in  cold  than  in  hot  water,  and  the 
result  of  raising  the  temperature  is  to  cause  the  deposit  of  the 
lime  on  the  heating  surfaces.  The  boiler  of  the  locomotive 
becomes  "  furred  "  like  the  inside  of  the  domestic  tea-kettle. 
The  lime  is  not  only  an  exceedingly  bad  conductor  of  heat,  but 
there  is  reason  to  believe  that  its  emissive  powers  are  also 
low,  and  a  very  moderate  thickness  of  it  accumulated  on  a  fire- 
box plate  will  secure  the  overheating  and  more  or  less  rapid 
destruction  of  that  plate.  It  is  held  by  some  persons  that  if 
the  circulation  is  rapid,  deposit  will  not  have  time  to  attach 
itself  to  the  metal.  This  is,  but  only  in  a  very  small  way,  true. 
It  holds  good  of  water-tube  boilers — provided  the  tubes  are  short 
in  proportion  to  the  diameter,  and  the  water  is  not  heavily 
charged  with  lime  ;  but  there  is  no  circulation  round  a  locomotive 
fire-box  powerful  enough  to  save  the  situation.  The  true  way 
out  of  the  difficulty  lies  in  getting  rid  of  the  lime  before  it  enters 
the  boiler.  On  a  few  railways,  however,  much  good  has  been 
done  by  change  of  water.  Thus,  when  locomotives  are  worked 
for  some  time  in  a  district  where  the  water  is  bad,  they  are  then 
sent  to  another  district  where  the  water  is  soft  and  good.  In 


WATEE  159 

two  or  three  days  the  deposit  will  be  loosened  by  the  soft  water 
and  can  be  washed  out  as  mud.  Locomotive  boilers  are  always 
washed  out  at  intervals  of  two  or  three  days,  or  a  week,  or  even 
more,  according  to  the  quality  of  the  water,  as  will  be  explained 
when  the  daily  life  of  an  engine  is  dealt  with. 

A  long  account  of  the  chemistry  of  water-softening  would  be 
quite  out  of  place  here.  It  will  be  enough  to  say  that  lime  is 
kept  in  solution  in  the  water  by  the  presence  of  free  carbonic 
acid,  C02-  If  now  more  lime  is  added,  the  acid  is  neutralised 
and  the  whole  of  the  lime,  namely  that  originally  in  the  water 
and  that  added,  are  thrown  down  together  in  settling  tanks. 
Various  systems  are  employed. 

The  general  principle  of  neutralising  free  carbonic  acid  must 
be  modified  in  various  ways  to  suit  special  conditions.  What 
will  do  very  well  for  the  treatment  of  the  water  supply  of  a  large 
town,  where  space  for  filtering  tanks  and  plenty  of  time  are 
available,  will  not  suit  railways.  Lime  must  be  supplemented, 
usually  with  caustic  soda  or  soda  ash,  and  the  water  must  be 
heated  to  secure  rapidity  of  action.  The  system  devised  by 
Messrs.  Archbutt  and  Deeley,  and  used  on  the  Midland  Bail- 
way,  may  be  taken  as  typical.  The  process  is  completed  in 
about  three  hours,  so  that  only  comparatively  small  settling 
tanks  are  required.  The  water  is  sent  in  by  an  injector  and 
mixed  with  a  solution  of  slacked  lime  and  soda  ash  which  have 
been  boiled  together.  Air  is  blown  by  another  injector  through 
a  series  of  perforated  pipes  at  the  bottom  of  the  tanks  which 
effects  a  thorough  mixture,  not  only  of  the  reagents,  but  of  the 
mud  left  in  the  tank  with  the  fresh  water.  This  mud  seems  to 
cling  to  the  new  deposit  and  carry  it  down  to  the  bottom  of 
the  tanks  as  soon  as  the  blowing  in  of  air  ceases.  The  softened 
water  is  drawn  off  from  the  surface  by  a  floating  delivery  pipe, 
and  has  subsequently  a  small  quantity  of  carbonic  acid  from  a 
coke  fire  blown  into  it,  to  prevent  any  trifling  percentage  of 
lime  which  may  remain  in  the  water  from  settling  in  the  feed- 
pipes or  injector  nozzles  of  the  engines.  From  time  to  time 
the  sludge  which  accumulates  in  the  tanks  is  cleared  out. 

In  some  cases  where  the  water  is  fairly  good  much  benefit  is 


160  THE   KAIL  WAY  LOCOMOTIVE 

derived  from  putting  a  few  pounds  of  caustic  soda  into  the 
tender  tank  every  day.  Quite  a  small  quantity  suffices  to 
render  the  deposit  in  the  boiler  soft,  so  that  it  can  be  readily 
washed  out. 

Assuming  that  the  water  is  sufficiently  purified,  we  have  next 
to  consider  what  is  the  best  way  of  putting  it  into  the  boiler. 
This  does  not  refer  to  the  pump  or  injector  by  which  the  feed 
water  is  forced  in — apparatus  which  will  be  dealt  Avith  further 
on — but  to  the  locality  of  its  introduction.  The  following  state- 
ment, made  by  Mr.  James  Stirling  at  a  meeting  of  the  Insti- 
tution of  Mechanical  Engineers,  in  the  course  of  the  discussion 
on  Mr.  Churchward's  paper  on  "  Large  Locomotive  Boilers," 
read  in  February,  1906,  covers  most  of  this  ground  and  is 
highly  suggestive : — 

"  With  regard  to  feed- water,  he  believed  he  had  fed  water  into 
locomotive  boilers  in  almost  every  way  possible  to  think  of.  He 
had  delivered  it  through  the  smoke-box  tube  plate,  sending  it 
straight  back  to  the  fire-box  under  the  impression,  as  was 
natural,  that  the  ebullition  being  most  violent  at  the  top  of  the 
fire-box  and  in  the  immediate  neighbourhood  of  the  tube  plate, 
that  the  current  of  water  must  necessarily  flow  to  the  smoke-box 
end  and  come  back  to  the  fire-box  under  the  tubes  ;  the  results 
were  very  satisfactory  as  to  steaming.  The  next  thing  was  to 
deliver  the  water  over  the  top  of  the  fire-box  in  front  of  the 
tube  plate,  but  that  only  created  fouling  of  the  tubes  where  they 
could  not  be  got  at  in  washing  out.  He  then  fed  the  water  in  at 
either  side  of  the  fire-box,  with  the  result  that  all  the  stays  began 
to  leak  forthwith.  The  next  and  the  last  thing  was  to  feed  the 
water  in  the  old-fashioned  place,  namely,  in  the  side  of  the  first 
plate  from  the  smoke-box  of  the  boiler,  and  he  there  had  a 
'command  of  the  fouling,  and  could  get  the  hose-nozzle  at  it  on 
washing-out  days  and  clear  it  away ;  in  that  way  he  managed  to 
keep  his  boilers  fairly  clean.  Those  dealing  with  locomotive 
boilers  knew  that  the  moment  the  water  reached  the  heat  it 
immediately  precipitated  any  lime  or  deleterious  matter  that 
might  be  in  it." 

If  cold  water  is  sent  into  a  boiler  it  can  do  much  harm  by/ 


WATER  161 

setting  up  local  contractions,  and  so  causing  leakage.  That  is 
the  explanation  of  the  fact  stated  above,  that  when  the  feed  was 
put  in  at  the  sides  of  the  fire-box  the  stay  bolts  leaked.  An 
attempt  is  often  made  to  raise  the  temperature  before  the  water 
enters  the  boiler,  both  to  save  the  plates  and  to  economise  fuel. 
As  far  back  as  1850  a  pipe  was  carried  from  the  boiler  to  the 
bottom  of  the  tender  tank ;  when  steam  began  to  blow  off  at  the 
safety  valve,  a  cock  in  this  pipe  was  opened  and  the  steam 
blown  into  the  tank,  thus  raising  the  temperature  of  the  feed 
water  and  avoiding  waste.  Subsequently  Mr.  Stroudley  turned 
a  portion  of  the  exhaust  steam  into  the  tender.  Mr.  Drummond 
has  a  special  apparatus  for  this  purpose,  the  description  of  which 
must  be  postponed  until  tenders  are  dealt  with. 

The  injector,  which  will  be  described  presently,  always  raises 
the  temperature  of  the  feed.  Sometimes  the  feed  pipe  is  carried 
along  inside  the  boiler  for  several  feet,  the  temperature  of  the 
feed  water  inside  rising  within  it.  The  true  solution  of  the 
difficulty,  however,  lies  in  sending  the  feed  water  into  the  steam 
space  as  spray.  It  can  then  exert  no  chilling  effect,  and  much 
if  not  all  the  lime  will  be  deposited  as  a  fine  powder  which  can 
be  washed  out.  Experiments  made  in  this  direction  have  been 
quite  successful.  There  is,  however,  what  may  be  termed  a 
popular  delusion  that  if  cold  spray  were  turned  into  the  steam 
space  it  would  at  once  condense  all  the  steam.  This  is  quite  a 
mistake.  A  small  quantity  of  steam  would  undoubtedly  lose  its 
heat,  but  the  boiler  would  at  once  replace  the  steam  condensed, 
and  the  net  effect  on  the  quantity  of  steam  available  for  the 
engines  in  any  unit  of  time  will  be  the  same,  whether  the  cold 
water  goes  into  hot  water  or  into  the  steam  space.  An  equally 
grave  error  is  based  on  an  erroneous  theory  of  the  injector,  accord- 
ing to  which  the  injector  cannot  send  water  into  steam.  It  will 
be  shown  further  on  that  the  injector  will  work  equally  well  no 
matter  into  what  the  water  is  forced.  Mr.  Churchward  has  been 
carrying  out  experiments  on  the  Great  Western  Railway  on  the 
introduction  of  feed  water  into  the  steam  space ;  certain  con- 
structive difficulties  have  been  encountered,  but  nothing  affecting 
the  soundness  of  the  principle. 

R.L.  M 


CHAPTER  XXI 

PRIMING 

NOTHING  has  been  said  so  far  about  the  quality  of  the  steam. 
To  the  general  public  no  doubt  all  steam  is  the  same.  But  the 
engineer  understands  that  the  quality  of  steam  has  a  wide  range. 
Good  steam  is  almost  entirely  free  from  water  and  dirt,  and  can 
only  be  had  from  clean  water,  heated  in  a  clean  boiler.  Bad 
steam  is  wet — "  priming  "  goes  on  in  the  boiler.  The  water  in 
the  boiler  is  dirty,  and  so  is  that  in  the  steam — doubly  or  trebly 
dirty.  The  steam  may  carry  with  it  fine  mud,  fine  sand,  now 
and  then  hard  lime,  which  has  a  disastrous  effect  on  the  engines. 
But  even  when  the  water  is  clean,  if  a  boiler  is  hard  pressed 
priming  may  take  place,  and  to  such  an  extent  that  the  trains 
cannot  keep  time.  The  causes  of  priming  are  very  imperfectly 
understood.  A  small  quantity  of  oil  or  grease  in  the  feed  water 
will  make  the  water  "  foam,"  and  priming  will  go  on  until  the 
grease  has  been  got  rid  of.  On  the  other  hand,  in  the  old  days 
before  surface  condensers  were  used,  aiid  marine  boilers  were  fed 
with  sea  water,  syringes  were  carried  which  could  be  screwed  on 
to  small  clack-valve  boxes  near  the  water  level,  and  melted 
tallow  was  forced  into  the  boiler  which  was  giving  trouble,  and 
almost  always  stopped  the  priming. 

Although  a  clean  boiler  will  not  prime,  the  water  always  lifts 
in  a  locomotive  boiler  while  the  throttle  valve  is  open,  It  is  for 
this  reason  that  while  a  locomotive  is  running,  the  glass  water 
gauges  are  almost  always  full  to  the  top.  When  steam  is  shut 
off  ebullition  ceases  at  once  for  the  time,  and  the  water  falls  a 
couple  of  inches.  The  steam  space  in  a  locomotive  is  restricted, 
and  two  different  systems  are  used  to  get  dry  steam.  According 
to  the  first,  the  entrance  to  the  pipe  which  supplies  the  cylinders 


PEIMING  163 

is  placed  as  far  above  the  level  of  the  water  as  possible  in  a  dome 
on  the  top  of  the  boiler.  According  to  the  second  system,  the 
steam  pipe  runs  the  whole  length  of  the  barrel  of  the  boiler, 
quite  close  to  the  top,  and  in  the  top  of  the  steam  pipe  are 
drilled  small  holes,  or  else  a  number  of  transverse  cuts  are  sawn 
in  it,  through  which  the  steam  has  to  enter,  the  rear  end  of  the 
pipe  being  stopped  up  by  a  plug  screwed  in.  In  this  way  the 
steam  being  drawn  not  from  one  spot,  but  from,  so  to  speak,  the 
whole  steam  space,  the  lifting  of  the  water  is  diminished,  and 
the  steam  kept  dry.  The  perforated  pipe  has,  however,  gone 
out  of  use,  not  so  much  because  it  was  inefficient  as  because 
the  regulator  or  throttle-valve  box  has  to  be  placed  in  the 
smoke-box,  where  it  is  not  wanted,  and  is  indeed  very  much  in 
the  way. 

It  may  be  asked,  How  is  it  known  that  a  boiler  is  priming  ? 
When  the  priming  is  profuse  there  can  be  no  doubt  about  it, 
because  hot  water  is  blown  through  the  cylinders  out  of  the 
chimney.  But  there  a,re  all  degrees  of  priming,  from  a  fraction 
of  1  per  cent,  up,  and  a  good  deal  of  ingenuity  has  been 
expended  in  devising  means  of  measuring  the  amount  of  pure 
water  in  any  stated  volume  of  steam.  It  cannot,  however,  be 
said  that  the  results  are  quite  satisfactory.  In  point  of  fact,  the 
precise  estimation  of  water,  or  degree  of  wetness  of  steam,  is 
very  far  from  easy,  because  a  great  many  chances  of  error  have 
to  be  guarded  against.  Three  different  methods  have  been  tried. 
The  first  and  simplest  consists  in  putting  a  good  deal  of  salt  into 
the  boiler,  and  then  condensing  a  known  weight  of  steam  drawn 
from  the  main  steam  pipe.  If  the  boiler  primes  it  must  prime 
salt  water.  The  water  resulting  from  the  condensation  of  the 
steam  is  evaporated  in  a  shallow  pan,  and  the  salt  left  at  the 
bottom  is  weighed.  A  simple  calculation  too  obvious  to  need 
stating  then  gives  the  percentage  of  water  in  the  steam.  The 
fundamental  objection  is  that  the  presence  of  the  salt  may  itself 
set  up  priming,  and  is  besides  bad  for  the  boiler.  A  refinement 
of  the  process  consists  in  using  very  little  salt  and  adding  to  the 
condensed  steam  in  a  test  tube  a  solution  of  nitrate  of  silver, 
which  if  salt  be  present  gives  a  curdy  or  flocculent  deposit.  The 

M2 


164  THE  RAILWAY  LOCOMOTIVE 

system  has  been  used  to  a  limited  extent  with  water-tube,  but 
never  with  locomotive  boilers. 

The  second  system  seems  to  have  been  first  used  some  thirty 
years  ago  by  Mr.  Barrus,  an  American  engineer.  The  principle 
involved  is  very  simple.  The  total  heat  in  a  pound  of  steam  is 
much  greater  than  the  total  heat  in  a  pound  of  water  of  the  same 
temperature.  If  now  we  turn  any  known  weight  of  steam  into 
cold  water  the  temperature  of  the  water  will  be  raised,  and  the 
drier  the  steam  the  greater  will  be  the  rise  in  temperature.  Thus 
the  total  heat  in  one  pound  of  steam  at  an  absolute  pressure  of 

165  Ibs.— boiler  pressure  150  Ibs.— is  1192'9  from  water  at   32° 
F.  and  the  total  heat  in  water  of  the  same  temperature  is  866°. 
Now  if  we  condensed  one  pound  of  steam  to  water  at  32°,  1192'9 
British  thermal  units  would  be  given  up.     If  we  cool  down  one 
pound  of  water  through  the  same  range  of   temperature,  366 
thermal  units  will  be  given  up,  and  any  mixture  of  the  water  and 
the  steam   will  give  up  less  than  the  one  and  more  than  the 
other.     So  if  we  mix  one  pound  of  steam  with  one  pound  of  water 
the  total  available  heat  will  be  1192*9+366=1529  units,  whereas 
if  the  two  pounds  of  fluid  drawn  from  the  boiler  had  been  pure 
dry   steam   there  would  have  been  2,386  units  available.     All 
we  have  to  do  then,  is  to  ascertain  how  much  less  than  1,193  units 
is  given  up  by  each  pound  of  steam  drawn  from  the  boiler,  and 
a   very  simple   calculation  will   give   the  percentage   of   water 
present. 

In  practice  a  small  wooden  cask  is  placed  near  the  boiler  on 
the  platform  of  a  weighing  machine  ;  in  the  cask  is  a  known 
weight  of  water.  The  temperature  is  taken  by  a  thermometer. 
Communicating  with  the  boiler  or  the  main  steam  pipe  is  a 
tube  fitted  with  a  stop  cock.  To  the  end  of  this  tube  is 
attached  a  piece  of  india-rubber  piping.  All  being  ready,  and 
weights  being  placed  in  the  scale  to  overbalance  the  cask  and 
its  contents  by  a  certain  amount,  steam  is  blown  through  the 
pipe  to  warm  it  up  and  clear  it  of  condensed  steam.  The  end 
of  the  india-rubber  pipe  is  then  plunged  into  the  water  in  the 
cask  and  steam  is  allowed  to  flow  until  enough  of  it,  say  5  Ibs. 
or  10  Ibs.  or  20  Ibs.,  has  been  condensed  to  turn  the  scale.  The 


PRIMING  165 

steam  cock  is  then  closed.  The  rise  in  emperature  and  the 
increase  in  weight  are  carefully  noted,  and  a  simple  calculation 
gives  the  percentage  of  priming.  An  improved  form  of  apparatus 
was  devised  by  Mr.  Barrus,  but  the  chances  of  error  are  so  great 
that  it  is  impossible  to  regard  the  results  as  certainly  correct 
within  3  per  cent. 

The  Barrus  system  has  been  entirely  superseded  by  the 
throttling  calorimeter  invented  by  Mr.  Peabody,  also  an  American 
engineer,  which  with  care  will  give  very  accurate  results.  It 
depends  for  its  action  on  entirely  different  phenomena. 

If  the  reader  will  turn  to  the  table  of  the  properties  of  steam 
given  on  page  152,  he  will  see  that  as  the  pressure  and 
temperature  rise,  so  does  the  total  heat,  only  very  much  more 
slowly.  Let  us  take,  as  before,  our  pound  of  pure  dry  steam  at 
165  Ibs.  Its  total  heat  we  have  seen  is  1,193°  F.  Let  now  this 
steam  fall  in  pressure,  without  doing  any  work,  to  that  of  the 
atmosphere  ='  14'7  Ibs.  Its  temperature  will  then  be  212°  F., 
and  its  total  heat  1,146°  JF.,  and  we  have  1193°  -  1146°  F.  The 
difference  is  47°.  What  becomes  of  this  ?  Kankine  was  the  first 
to  show  that  if  the  steam  contained  no  free  water  the  47°  F. 
would  superheat  it.  We  may  further  deduce  that  if  it  did 
contain  water  then  that  water  would  be  all  converted  into  steam 
unless  there  was  too  much  of  it.  If  the  reader  has  followed  so 
far  he  will  have  no  difficulty  now  in  seeing  that  it  is  only 
necessary  to  take  the  temperature  of  the  steam  before  and  after 
the  fall  in  pressure  to  ascertain  the  percentage  of  water  present. 
As  the  specific  heat  of  steam,  that  is  to  say,  the  quantity  of  heat 
required  to  raise  it  one  degree  Fahrenheit  in  temperature,  is  to 
that  of  water  as  *48  to  1,  the  47°  available  would  raise  the 
temperature  of  one  pound  of  steam  by  nearly  twice  as  much.1 
The  calorimeter  in  its  most  improved  form  is  illustrated  by 
Fig.  57. 

The  steam  is  allowed  to  expand  without  doing  any  work  by 

1  The  true  value  of  the  specific  heat  of  steam  cannot  be  regarded  as  settled ; 
inquiry  is  still  proceeding.  There  is  reason  to  believe  that  it  varies  with 
the  pressure.  The  figure  given  is,  however,  quite  accurate  enough  for  the 
present  purpose. 


166 


THE   RAILWAY  LOCOMOTIVE 


passing  through  a  small  orifice  in  a  thin  plate  at  I.  The  main 
steam  pipe  is  shown  at  G,  and  the  collecting  pipe  atF.  It  enters 
the  steam  pipe  as  shown,  and  much  discussion  has  taken  place 
as  to  the  best  way  to  admit  the  steam  into  F.  With  this  we 
need  not  concern  ourselves.  A  is  a  so-called  drip  box,  which  is 
intended  to  remove  some  of  the  priming  water  if  it  is  plentiful. 
This  is  collected  and  measured,  its  height  in  the  drip  box  being 


FIG.  57.— The  Peabody  calorimeter. 

shown  by  the  glass  water  gauge  C.  The  discharge  cock  is  shown 
at  D.  The  steam  passes  from  the  top  of  the  drip  box  by  E  P 
into  K,  into  which  is  screwed  the  thermometer  M.  The  thin 
plate  is  shown  by  E.  J  and  S  are  flanges  between  which  E  is 
bolted.  The  expanded  steam  passes  through  0  into  L  and  thence 
into  the  atmosphere.  N  is  a  thermometer  similar  to  M.  The 
difference  between  the  reading  of  the  two  thermometers  expresses 
the  quality  of  the  steam,  in  other  words  the  percentage  of  water 
in  it.  It  is  not  necessary  to  give  here  a  general  equation.  In 
practice,  nothing  in  the  way  of  an  elaborate  calculation  is 


PEIMING  167 

necessary.  Mr.  Barrus  gives  in  Vol.  XI.  of  the  Transactions  of 
the  American  Society  of  Mechanical  Engineers  the  following 
instructions  for  using  this  instrument : — 

"  In  order  to  compute  the  amount  of  moisture  from  the  loss  of 
temperature  shown  by  the  heat  gauge,  the  number  of  degrees  of 
cooling  of  the  lower  thermometer  (N)  is  divided  by  a  certain 
co-efficient,  representing  the  number  of  degrees  of  cooling  due  to 
1  per  cent,  of  moisture.  This  co-efficient  depends  upon  the 
specific  heat  of  superheated  steam,  which,  according  to  Eegnault's 
experiments,  is  0'48.  In  other  words,  the  heat  represented  by 
1°  of  superheating  is  0'48  of  a  thermal  unit.  This  quantity 
cannot  be  applied  exactly  to  the  form  of  instrument  under  con- 
sideration. The  quantity  to  be  used  varies  somewhat  according 
to  the  degree  of  moisture.  For  an  instrument  working  under  a 
temperature  of  314°  F.,  by  the  upper  thermometer,  and  with  a 
cooling  by  the  lower  thermometer  from  268°  to  241°,  the 
quantity  was  found  to  be  about  0*42.  When  the  cooling,  however, 
was  from  266°  to  225°,  the  quantity  to  be  used  was  found  to  be 
about  0*51.  The  experiments  have  not  as  yet  covered  a  sufficient 
range  to  determine  the  exact  law  which  can  be  applied  to  every 
case,  but  it  seems  probable  that  the  specific  heat  is  more  or  less 
constant  until  the  temperature  by  the  lower  thermometer 
approaches  the  point  of  saturation  for  the  low  pressure  steam, 
while  beyond  this  point  the  specific  heat  rapidly  increases.  For 
the  present,  it  is  assumed  that  the  quantity  O42  is  the  proper 
one  to  apply  whenever  the  temperature  by  the  lower  thermometer 
is  above  235°,  and  that  in  cases  where  the  temperature  is  below 
235°,  the  quantity  to  be  used  is  an  increasing  one,  reaching 
perhaps  to  0*55  when  the  temperature  drops  to  220°. 

"  One  per  cent,  of  moisture  now  represents  the  quantity  of  heat 
determined  by  multiplying  the  latent  heat  of  one  pound  of  steam, 
having  a  pressure  corresponding  to  the  indication  of  ther- 
mometer M,  by  O'Ol,  and  this  product  is  to  be  divided  by 
0'42  (provided  the  lower  temperature  is  not  below  233°)  in 
order  to  express  it  in  terms  of  degrees  of  superheat.  For 
example:  when  thermometer  M  shows  312°,  the  latent  heat 
is  894  thermal  units,  and  1  per  cent,  of  this  is  8'94 ;  dividing 


168 


THE   KAIL  WAY  LOCOMOTIVE 


by.0'42,  the  number  of  degrees  of  superheat  corresponding  to 
1  per  cent,  of  moisture  is  found  to  be  21 '3.  For  several 
other  temperatures,  which  cover  the  ordinary  range  that  would 
commonly  be  used,  the  necessary  co-efficient  is  given  in  the 
following  table : — 


Temperature  by  Ther- 
mometer M. 

Co-efficient. 

Temperature  by  Ther- 
mometer M. 

Co-efficient. 

270 

22-0 

320 

21-1 

280 

21-8 

330 

21-0 

290 

21-7 

340 

20-8 

300 

21*5 

350 

20  6 

310 

21-3 

360 

20-5 

Certain  corrections  have  to  be  made  for  radiation  from  the 
calorimeter  itself,  and  curiously  enough  it  has  been  found  that 
when  the  steam  is  very  wet  so  much  water  remains  in  the  drip 
box  that  the  steam  going  into  the  instrument  proper  is  actually 
drier  than  is  steam  which  does  not  deposit  any  sensible  quantity 
in  the  drip  box." 


CHAPTER  XXII 


THE    QUALITY    OF    STEAM 

WE  may  now  turn  to  the  results  obtained  in  practice  from  the 
modern  locomotive  boiler  as  ascertained  by  the  calorimeter.  In 
this  country  nothing  has  been  done  in  this  way.  Indeed,  the 
only  information  on  this  point  which  covers  a  sufficiently  wide 
range  of  locomotives  has  been  supplied  by  tests  carried  out  at 
the  St.  Louis  Exhibition  of  1904,  to  which  reference  has  already 
been  made  in  these  pages.  The  importance  of  the  figures  will 
be  better  appreciated  when  we  come  to  deal  with  superheating 
and  its  effects  on  the  economical  efficiency  of  locomotives. 

It  is  very  constantly  assumed  that  locomotive  engine  boilers 
do  not  supply  dry  steam.  That  is  to  say,  it  is  asserted  that  it 
never  contains  less  than  5  per  cent,  of  water.  The  St.  Louis 
experiments  do  not  bear  out  this  proposition.  In  all  eight  engines 
were  tested ;  of  these  four  were  passenger  and  four  were  goods 
engines.  The  following  table  gives  the  results  of  tests  made 
with  the  Peabody  throttling  calorimeter  just  described :— 


Loco.  Number. 

Maximum. 

Minimum. 

GOODS. 

1499 

•9903 

•9877 

734 

•9871 

•9837 

9129 

•9846 

•9445 

585 

•9845 

•9828 

PASSENGER. 

628 

•9986 

•9936 

2512 

•9859 

•9812 

3000 

•9835 

•9499 

585 

•9823 

•9626 

170  THE  EAILWAY  LOCOMOTIVE 

The  decimals  express  the  percentage  of  steam  in  ten  thousand 
parts  of  the  mixture  of  steam  and  water  supplied  by  the  boiler. 
The  maximum  percentage  of  water,  it  will  be  seen,  is  about  5*5, 
the  minimum  a  shade  over  1  per  cent.  It  must  not  be  forgotten 
that  these  results  were  obtained  from  very  dissimilar  boilers 
working  under  dissimilar  conditions,  and,  therefore,  may  be 
taken  as  thoroughly  representative.  But  it  must  also  be  kept 
in  mind  that  the  boilers  were  very  clean,  and  were  supplied  with 
water  of  excellent  quality. 

A  complete  explanation  of  the  causes  of  priming  has  not  yet 
been  framed ;  why,  for  example,  dirty  water  should  prime  and 
clean  water  will  not  is  not  known.1  The  theory  of  the  matter 
is  that  surface  tension  has  something  to  do  with  it.  This  means 
that  the  bubbles  of  steam  have  a  comparatively  tough  envelope 
of  water,  which  rises  through  the  main  body.  When  the  bubble 
bursts  this  water  is  scattered  in  all  directions,  and  remains 
suspended  in  the  steam.  Again,  when  water  is  boiling  in  an 
open  vessel  it  will  be  seen  that  a  multitude  of  little  fountains  of 
spray  rise  from  the  surface  and  fall  back  again.  The  water  in 
these  may  be  readily  entrained  and  carried  away  by  the  steam 
if  there  is  a  strong  current  moving  in  any  particular  direction, 
as,  for  example,  to  the  opening  of  the  regulator. 

1  Water-tube  boilers  supplied  with  pure  clean  rain  water  will  prime,  and 
with  distilled  water  will  not.  Locomotive  type  boilers  supplied  to  H.M.S. 
Polypheffiut  primed  so  much  on  board  that  they  had  to  be  taken  out.  They 
were  worked  with  water  from  surface  condensers.  They  were  subsequently 
put  up  on  land  and  used  for  driving  dockyard  machinery  with  similar  water, 
and  gave  no  trouble  whatever.  Abundant  examples  of  the  capriciousness 
of  boilers  could  be  supplied. 


CHAPTEK   XXIII 

SUPERHEATING 

A  CONSIDERATION  of  how  far,  and  in  what  way,  the  economical 
and  absolute  efficiency  of  a  locomotive  are  affected  by  the  quality 
of  the  steam  must  be  postponed  until  we  come  to  deal  with  the 
engines.  It  is  open,  perhaps,  to  question  whether  superheaters 
are  part  of  the  boiler  or  part  of  the  engine.  The  author  holds 
it  to  be  most  convenient  to  adopt  the  first  view,  and  to  regard  all 
that  affects  the  quality  of  the  steam  as  delivered  to  the  engine  as 
part  of  the  generating  apparatus. 

Before  describing  superheaters  it  is  necessary  to  explain  what 
they  are  intended  to  do. 

It  will  be  understood  from  what  has  gone  before  that  saturated 
steam  is  an  unstable  fluid.  It  is  not  easy,  indeed,  to  realise  how 
unstable.  It  is  always  on  the  point  of  reverting  to  its  original 
condition  of  water.  Now,  when  any  percentage  of  a  given  weight 
of  steam  liquefies  it  surrenders  all  its  latent  heat,  and  if  only  the 
heat  could  be  utilised,  then  liquefaction  might  do  very  little 
harm.  It  can  be  shown,  however,  that  such  utilisation  does 
not  take  place  in  practical  work ;  and  it  becomes  expedient, 
therefore,  to  impart  stability  to  the  steam.  If  we  reduce  the 
temperature  of  dry  saturated  steam  by  withdrawing  heat  some 
of  it  will  condense.  If,  however,  the  steam  possesses  a  sensible 
temperature  greater  than  that  due  to  its  pressure,  then  no  con- 
densation can  take  place  until  such  a  time  as  the  whole  of  this 
additional  temperature  has  been  withdrawn.  Thus,  let  us  suppose 
the  case  of  one  pound  of  steam,  with  an  absolute  pressure  of 
165  Ibs.  per  square  inch.  Its  temperature  is  366°  F.,  the  total 
quantity  of  heat  in  it  is  1,193°,  its  volume  is  2'71  cubic  feet. 
If  nowr  we  withdraw  nominally  one-tenth  of  the  total  heat,  then 


172  THE   EATLWAY  LOCOMOTIVE 

one-tenth  of  the  steam  will  be  reduced  to  the  condition  of  water, 
and  so  on.  But  0*1  means  119°,  omitting  fractions.  If,  however, 
we  had  added  to  the  steam  beforehand  the  equivalent  (depending 
for  its  amount  on  the  specific  heat)  of  119°,  then  the  withdrawal 
of  one-tenth  might  take  place — there  would  be  a  reduction  in 
temperature,  but  no  condensation.  This  is  the  principle  on  which 
the  value  of  superheating  depends. 

The  figures  given  above  must  be  regarded  only  as  illustrative, 
for  the  conditions  of  superheating  are  much  more  complex  than 
may  appear  at  first  sight.  Thus,  one  of  the  immediate  effects 
of  superheating  is  to  increase  the  volume  of  the  body  of  steam 
superheated1;  it  has  been  shown  by  Fairbairn  that  the  volume 
augments  much  more  rapidly  at  first  than  it  does  sub- 
sequently. One  explanation  of  this  fact  is  that  the  water 
suspended  in  the  steam  is  evaporated  first  and  that  the  steam 
so  produced  goes  to  add  to  the  volume,  and  that  once  that  has 
been  effected,  expansion  takes  place  purely  as  if  the  steam  were 
a  gas.  Again,  as  has  been  already  pointed  oat  above,  consider- 
able uncertainty  exists  as  to  what  the  precise  specific  heat  of 
steam  gas  is.  Probably  it  is  about  *48°,  or  rather  less  than  one- 
half  that  of  water.  The  specific  heat  of  dry  saturated  steam  is 
•305°,  that  is,  the  quantity  by  which  the  total  heat  of  saturated 
steam  is  increased  for  each  one  degree  of  added  temperature. 
The  expression  *305  is  used  in  a  compound  sense,  taking  account 
as  it  does  of  the  changes  both  of  volume  and  pressure  which 
take  place  in  the  generation  of  saturated  steam.  Kegnault's 
experiments  gave  the  specific  heat  of  steam-gas — that  is  to  say, 
of  steam  out  of  contact  with  water  in  any  shape — as  "475  under 
constant  pressure,  or  upwards  of  one-half  more  than  that  of 
saturated  steam.  Eecent  researches,  however,  seem  to  prove 

1  A  sharp  difference  of  opinion  exists  among  engineers  as  to  whether  the 
increase  of  volume  has  or  has  not  any  economic  value.  On  one  side  it  is 
maintained  that  such  a  reduction  of  temperature  always  takes  place  in  the 
engine  that  the  increase  of  volume  disappears ;  on  the  other,  an  eminent 
authority,  Dr.  v.  Garbe,  of  the  Prussian  State  Railways,  and  the  apostle  of 
the  Schmidt  system,  maintains  that  superheating,  or,  as  he  calls  them,  "  hot 
steam,  locomotives,"  must  have  larger  cylinders  than  saturated  steam  loco- 
motives in  order  to  utilise  this  augmented  volume. 


SUPERHEATING  173 

that  the  more  correct  co-efficient  is  '48.  To  complete  this  state- 
ment, Eankine  lays  it  down  that  the  total  heat  required  to 
convert  a  given  substance  from  a  state  of  great  density  at  a 
given  temperature,  To,  to  the  perfectly  gaseous  state  at  a  given 
temperature,  TI — the  operation  being  completed  under  any 
constant  pressure — is  given  by  the  equation 
h  =  a  +  c1  (Ti  --  To), 

where  a  is  a  constant  and  c1  is  the  specific  heat  of  the 
substance  in  the  perfectly  gaseous  state  under  constant  pres- 
sure. Thus,  to  convert  one  pound  of  water  at  32°  into  steam  - 
gas  at  212°  requires  '1092  +  '475  X  180  =  1,177  units  of 
heat,  being  more  than  the  quantity  required  to  make  saturated 

1  177 

steam  in  the  ratio  ,-      ^  =  1-028.      Here  a  —  1,092  and  c1  = 
l,14o 

•475. 

The  principal  utility  of  these  equations  lies  in  showing  how 
much  heat  must  be  added  to  steam  to  convert  it  into  a  compara- 
tively stable  gas.  In  so  far  as  regards  the  locomotive,  however, 
their  value  is  in  the  main  academical ;  because,  in  the  first 
place,  heat  which  would  otherwise  be  wasted  is  supposed  to  be 
utilised,  and  because,  in  the  second  place,  the  results  obtained 
in  practice  do  not  bear  any  traceable  relation  to  the  figures 
given.  The  conditions  are  far  too  complex  to  permit  such  rela- 
tions to  be  established.  In  a  word,  superheating  has  hitherto 
been  carried  out  by  rule  of  thumb/  derived  from  rough  experi- 
ments. The  general  result  is  that  no  matter  how  the  super- 
heating is  effected,  the  hotter  the  steam  the  better  in  so  far  as 
economy  of  fuel  is  affected.  As  to  its  effects  on  rubbing  surfaces 
in  the  engine,  that  is  another  story  to  be  told  further  on. 

Although  various  methods  of  superheating  have  been  devised 
and  even  patented,  there  is  only  one  in  use.  The  steam  flowing 
from  the  boiler  to  the  engine  is  made  to  pass  through  pipes  in 
which  its  temperature  is  raised.  Now  it  so  happens  that  while 
wet  steam  will  absorb  heat  rapidly,  dry  steam  will  not.  Indeed, 
it  is  by  no  means  easy  to  superheat  steam  beyond  some  30  or 
40  degrees.  To  make  the  superheating  apparatus  worth  having, 
however,  the  temperature  of  the  steam  should  be  raised  at  least 


174  THE  EAILWAY  LOCOMOTIVE 

200  degrees,  so  that  150  Ibs.  boiler  steam  must  have  a  tempera- 
ture of  866°  +  200°  —  566°  F.  But  Schmidt  wants  much 
more  than  this ;  he  likes  650  to  700  degrees.  Where  on  a  loco- 
motive engine  can  space  be  found  for  the  required  pipes  ?  Here 
the  inventor  comes  in.  Four  or  five  different  systems  have  been 
tried.  Of  these  only  one  appears  to  have  come  as  yet  into  any- 
thing like  regular  use,  namely,  the  Schmidt.  Several  others 
are  still  in  the  experimental  stage — the  Notkin,  American, 
Cockerill,  Cole  &  Vaughan,  and  Horsey  may  be  mentioned. 
It  will  suffice  if  we  confine  our  attention  to  the  system  first 
named,  because  so  far  it  is  the  only  one  in  regular  use.  It  was 
introduced  by  M.  Schmidt  on  the  Prussian  State  Eailways  as  far 
back  as  1898.  Originally  the  place  of  a  number  of  the  lower 
flue  tubes  was  taken  by  one  large  tube  about  a  foot  in  diameter. 
In  the  smoke-box  were  fitted  at  the  sides  inverted  (j  -tubes. 
These  were  cut  off  from  the  smoke-box  by  partition  plates.  The 
steam  was  taken  in  at  one  end  of  the  \J  -tubes  and  delivered  to 
the  engine  from  the  other  end,  superheated  by  the  hot  gas 
passing  through  the  large  tube,  and  rising  at  each  side  to  the 
top  of  the  smoke-box  and  thence  up  the  chimney.  The  arrange- 
ment was  not  very  successful,  and  has  been  superseded  by  one 
quite  different. 

This  cannot  be  better  described  than  in  the  words  of  Herr 
Eobert  Garbe,  Chief  Mechanical  Engineer  of  the  Prussian  State 
Kailways,  who  has  recently  dealt  with  the  whole  subject  in  a 
series  of  articles  contributed  to  the  Engineer.  It  will  be  seen 
from  Figs.  58,  59  and  60  that  the  ordinary  small  tubes  in  the 
upper  part  of  the  barrel  of  the  boiler  are  replaced  by  two  or  three 
rows  of  larger  size.  In  the  figures  there  are  three  rows  of  eight 
tubes  of  4-88  in.  internal  and  5'23  in.  external  diameter.  Within 
each  of  these  are  four  smaller  tubes  spaced  at  equal  distances, 
connected  together  at  their  fire-box  ends  by  cast  steel  return 
bends  to  form  a  single  continuous  passage,  so  that  the  steam 
passes  four  times  along  the  length  of  the  superheater  tubes. 
Near  the  fire-box  the  outer  tubes  are  contracted  to  4'48  in.  to 
allow  of  a  freer  movement  of  the  water  near  the  tube  plates,  into 
which  they  are  expanded  in  a  special  way.  The  ends  of  each 


SUPERHEATING 


175 


FIG.  60. 
The  Schmidt  superheater. 

group  of  superheater  elements  on  the  smoke-box  side  are 
expanded  into  flanges,  which  are  connected  to  the  steam  col- 
lecting box  by  screwed  joints  arranged  either  horizontally  or 


176  THE  EA1LWAY  LOCOMOTIVE 

vertically,  the  joint  being  made  tight  by  copper  asbestos  packings. 
The  former  arrangement  involving  a  semicircular  return  bend 
for  the  superheater  tubes,  has  the  disadvantage  of  requiring  an 
extra  long  smoke-box,  but  as  it  causes  a  better  utilisation  of 
the  heat  it  is  retained  on  the  Prussian  lines  up  to  the  present. 
The  cast  iron  superheated  steam  collector,  Fig.  60,  which  is 
made  of  the  same  metal  as  the  cylinders,  is  so  divided  and 
connected  with  the  boiler  and  the  valve  chest  that  the  steam 
from  the  former  must  pass  through  the  whole  of  the  superheater 
system  before  reaching  the  engine  cylinders.  The  fire  gases 
being  divided  between  the  lower  normally  arranged  boiler  tubes 
and  the  larger  upper  tubes  containing  the  superheaters,  give  up 
their  heat  partly  to  the  surrounding  boiler  water  and  partly  to 
the  steam  circulating  in  the  superheater.  The  regulation  of  the 
flow  of  the  gases  through  the  superheater  is  effected  by  a 
system  of  dampers,  which  are  kept  open  by  steam  pressure  as  long 
as  the  regulator  valve  is  open,  but  are  closed  when  the  latter  is 
shut  either  by  a  spring  or  a  counterweight.  "When  the  engine 
is  standing  or  running  without  steam  the  flame  is  entirely 
diverted  from  the  superheater  tabes,  which  would  otherwise 
become  red  hot.  The  position  of  the  dampers  can  also  be  varied 
while  the  engine  is  under  steam  by  a  hand  wheel  and  rod  on 
the  footplate,  so  that  the  superheating  may  be  regulated  inde- 
pendently of  the  automatic  arrangement.  The  latter,  placed 
outside  the  smoke-box  on  the  left-hand  or  fireman's  side,  is  a 
small  steam  cylinder  whose  piston  is  connected  by  levers  with 
the  damper  flaps.  There  is  a  pipe  connection  between  the  valve 
of  the  small  piston  and  the  valve  chest,  so  that  when  the  regu- 
lator is  open  and  steam  is  admitted  to  the  cylinders  the  piston 
travels  forward,  opening  the  dampers,  which  are  closed  by  the 
counterpoise  as  soon  as  the  pressure  is  taken  off  by  the  closing 
of  the  regulator. 

The  removal  of  soot  and  ashes  from  the  large  smoke  tubes 
may  be  most  readily  effected  by  steam  or  compressed  air  either 
from  the  fire-box  or  the  smoke-box,  but  preferably  from  the 
former.  As  a  rule,  air  at  ten  atmospheres  is  the  best  clean- 
ing agent  both  for  these  and  the  ordinary  boiler  tubes.  If 


SUPEBHEATING  177 

steam  is  used  the  cleaning  should  be  done  while  the  boiler  is 
still  hot. 

The  Notkin  superheater  is  very  similar  in  all  respects,  except 
that  instead  of  using  very  elongated  U -tubes  the  inventor  employs 
two  concentric  tubes,  placed  in  special  fire  tubes  3  inches  in 
diameter.  The  outer  concentric  tube  is  secured  to  one  half  of  a 
steam  chest  and  the  inner  tube  to  the  other  half.  The  steam 
passes  down  the  annular  space  between  the  two  tubes  from  one 
half  and  returns  up  the  centre  tube  to  the  other  half  of  the 
steam  chest,  whence  it  goes  on  to  the  cylinders. 

The  Pielock  superheater,  so  called  after  the  inventor,  has  been 
fitted  to  locomotives  on  the  Royal  Prussian  Bail  ways,  and  been 
tried  in  the  United  States.  It  consists  of  a  steel  chamber  placed 
in  the  barrel  of  the  boiler  far  enough  forward  to  prevent  the  tubes 
being  overheated.  Into  the  ends  of  the  box  the  boiler  tubes  are 
made  tight  by  rolling  them,  the  expander  being  placed  at  the 
end  of  a  long  steel  staff  which  passes  down  the  tubes.  It  is  not 
necessary  that  much  care  should  be  taken  to  make  the  joint 
tight,  as  the  pressure  is  nearly  the  same  inside  the  superheater 
and  outside.  It  is  only  required  that  the  water  shall  be  kept 
out.  The  box  is  divided  inside  by  diaphragm  plates  parallel  to 
the  tubes  in  order  that  circulation  may  be  secured  inside  it.  The 
steam  is  collected  at  the  top  of  the  dome,  passes  down  into  the 
superheater,  and  then  rises  again  to  the  regulator  valve  box  and 
thence  to  the  engine.  The  total  heating  surface  taken  inside  the 
tubes  in  a  normal  locomotive  is  1,753  square  feet,  the  total 
heating  surface  of  the  superheater  inside  is  283*79  square  feet  or 
•16  of  the  whole  tube  surface.  At  the  St.  Louis  Exhibition,  the 
quality  of  the  steam,  before  it  entered  the  superheater  at  all, 
was  excellent,  the  moisture  never  exceeding  one  half  per  cent. 
The  lowest  superheat  was  161°  F.  and  the  highest  192°  F. 
Curiously  enough,  the  amount  of  superheat  did  not  seem 
to  be  much  affected  by  different  rates  of  combustion  or 
evaporation.  The  explanation  is  that  when  more  steam  was 
passed  through  the  superheater  the  fire  was  hotter  and,  of 
course,  the  gas  in  the  tubes.  As  the  steam  pipe  from  the  super- 
heater passed  through  the  boiler  the  temperature  of  the  steam 

R.L.  N 


178  THE  RAILWAY  LOCOMOTIVE 

was  reduced.  It  is  clear,  therefore,  that  there  was  loss  of  heat 
before  the  steam  reached  the  engines.  The  Pielock  superheater 
is  fairly  efficient,  but  it  is  argued  about  it  that  on  the  whole  as 
much  in  the  way  of  evaporation  is  lost  as  the  superheater  can 
gain.  The  more  cogent  argument  against  it  is  said  to  be  the 
fact  that  the  flue  tubes  are  liable  to  rapid  corrosion  inside  the 
superheater. 

It  was  not  to  be  supposed  that  such  an  innovation  as  super- 
heating would  be  accepted  without  question,  and  very  keen 
discussions  have  taken  place  concerning  not  only  the  respective 
merits  of  various  systems,  but  the  theoretical  and  actual  value 
of  superheating.  When  superheating  was  first  proposed  in 
locomotives  it  was  maintained  that  the  heat  which  was  wasted 
up  the  chimney  could  be  utilised  and  in  this  way  superheating 
could  be  had  for  nothing.  It  was  very  soon  stated,  however,  that 
a  smoke-box  temperature  of  at  the  most  700  degrees  could  not 
raise  the  temperature  of  the  steam  to  anything  like  the  necessary 
amount.1  Therefore,  as  has  been  shown,  in  the  preliminary 
Schmidt  heaters,  a  large  proportion  of  the  gases  was  conveyed 
through  a  flue  tube  of  considerable  diameter  to  the  smoke-box. 
This  did  not  answer,  and  now  nearly  all  locomotive  superheaters 
save  the  Pielock  differ  from  each  other  only  in  details.  Into 
enlarged  flues  are  put  small  pipes,  one  end  of  each  pipe  receiving 
steam  from  the  boiler,  the  other  end  delivering  steam  to  the  engine. 
No  waste  heat  is  utilised.  The  steaming  power  of  the  boiler  is 
diminished  because  the  heating  surface  of  large  flue  tubes  is  less 
than  that  of  the  more  numerous  small  tubes  which  could  be  put 
into  the  same  space.  As,  however,  the  economic  efficiency  of  a 
boiler  is,  other  things  being  equal,  measured  by  the  smoke-box 
temperature,  and  this  does  not  appear  to  be  augmented  by  the 
presence  of  a  superheater,  it  may  be  taken  for  granted  that 
the  only  loss  incurred  will  be  in  the  ability  of  the  boiler  to  make 
steam.  This  means  that  an  engine  with  a  superheater  would 

1  It  is  however  claimed  that  the  Baldwin  smoke-box  superheater  raises 
the  temperature  as  much  as  is  really  necessary  with  the  waste  gas  only. 
The  claims  made  are  so  conflicting  as  regards  the  temperature  which  repre- 
sents all-round  maximum  economy  that  the  author  reserves  all  expressions 
ol  opinion  on  the  point. 


SUPEKHEATING  179 

not  be  able  to  draw  trains  as  heavy  or  as  fast  as  it  would  be 
without  the  superheater,  although  the  cost  of  coal  per  ton  per 
mile  might  remain  unaltered.  On  the  other  hand  superheated 
steam  being  more  efficient  than  ordinary  steam,  the  balance  is 
restored,  the  power  of  the  engine  is  increased,  and  an  economy 
of  fuel  effected.  How  much,  remains  a  bone  of  contention  among 
railway  engineers,  the  dispute  being  strengthened  by  the  lack  of 
uniformity  in  results  obtained  on  different  railways.  In  this 
country,  very  little  has  been  done,  because  it  is  maintained  that 
the  large  addition  to  the  first  cost  of  the  locomotive,  and  the 
heavy  expenditure  on  the  upkeep  of  an  apparatus  so  liable  to 
wear  and  tear  and  corrosion  cannot  fail  to  neutralise  much  of  the 
economical  advantage  that  it  may  be  able  to  bestow.  So  far  the 
experience  obtained  on  Continental  lines  has  not  been  regarded 
as  convincing.  The  size  of  the  smoke-box,  too,  is  increased,  as  is 
the  weight  on  the  leading  bogie.  The  kind  of  work  done  in  this 
country  is  different  in  many  respects  from  that  performed  by 
Continental  locomotives.  Our  coal  is  very  much  better,  and  on 
the  whole,  cheaper  ;  and  lastly,  we  have  the  somewhat  sentimental 
objections  held  by  British  engineers  to  anything  savouring  of 
complications,  which  are  for  the  most  part  favoured  rather  than 
condemned  in  Europe. 


CHAPTEE   XXIV 

.      BOILER    FITTINGS 

WE  come  now  to  the  several  adjuncts  or  appurtenances  with 
which  the  boiler  is  fitted.  Although  these  always  serve  the  same 
purpose  they  vary  widely  in  design  and  the  details  of  their  con- 
struction. None  of  them,  perhaps,  is  so  obvious  to  the  railway 


FIG.  61. — American  throttle  valve. 

traveller  as  the  regulator,  a  handle  on  the  back  plate  of  the  fire- 
box, which  seems  to  possess  a  magic  power  of  calling  the  enormous 
machine  into  life.  It  derives  its  name  from  its  function,  which 
is  to  open  or  shut  a  valve  inside  the  boiler,  which  controls  and 
regulates  the  supply  of  steam  to  the  cylinders.  When  the  boiler 
is  fitted  with  a  dome  of  any  kind,  this  valve  is  always  placed 
within  it.  When  there  is  no  dome  the  valve  is  placed,  as  a  rule, 
in  the  smoke-box.  If  not,  then  just  inside  the  front  tube  plate. 
The  valves  are  of  two  kinds.  They  are  either  double-beat 
valves,  or  sliding  valves.  The  first  type  is  almost  invariably 
used  in  the  United  States.  Figs.  61  and  62  give  the  general 
arrangement  and  a  section  to  an  enlarged  scale  of  an  American 
regulator  valve.  It  will  be  seen  that  the  valve  is  of  the  double- 
beat  equilibrium  type.  It  is  entirely  surrounded  by  steam, 


BOILER  FITTINGS 


181 


which  tends  to  force  the  upper  valve  down  on  its  seat  and  lift 
the  lower  valve  off  it.  A  bell-crank  lever  A  is  arranged  in  such 
a  way  that  by  pulling  on  the  lower  extremity  E  the  valve  is  raised 
from  its  seat,  and  steam  is  admitted  to  the  cylinders.  A  rod  E 
extends  from  the  bell-crank  lever  to  the  back  plate  of  the  fire- box, 
where  it  traverses  a  stuffing  box,  and  is  jointed  to  a  transverse 
lever  which  is  moved  by  the  engineman 
pushing  it  in  to  shut  off  steam ;  pulling 
it  out  turns  steam  on. 

The  "dry  pipe,"  that  is,  the  steam 
pipe  inside  the  boiler,  is  shown  at  F ; 
the  whole  valve  box  is  supported  inside 
the  dome  on  the  angle-iron  ring  B, 
Fig.  62,  by  a  flange  D,  Fig.  61.  At  B 
is  a  conical  ground  joint  fitting  a  seat  in 
a  flattened  portion  of  F.  The  surfaces 
are  drawn  together  steam  tight  by  the 
bolt  C.  The  fulcrum  of  the  bell  crank 
is  at  G. 

The  valves  are  not  perfectly  balanced, 
because  in  the  first  place  it  is  desirable 
that  there  should  be  a  tendency  to  keep 
the  valve  closed,  and  in  the  second,  the 
lower  valve  has  to  be  passed  through 
the  seating  of  the  upper  valve  to  get  it 
into  place.  In  the  valve  illustrated,  the 
upper  valve  is  6  inches  diameter  and 
the  lower  valve  5f  inches.  The  area  of  the  upper  valve  is  28*27 
square  inches,  that  of  the  bottom  valve  22'7  square  inches.  With 
a  boiler  pressure  of  200  Ibs.  the  top  valve  is  held  down  with  a 
force  of  about  5,654  Ibs.,  or  over  2*5  tons.  The  lower  valve, 
however,  tends  to  lift  off  its  seat  with  a  force  of  4,540  Ibs.  The 
difference  is  1,114  Ibs.,  and  at  first  sight  it  would  appear  that  the 
engine  driver  would  have  to  pull  very  hard  indeed  to  get  the 
valve  off  its  seat.  But  this  is  not  so.  In  the  first  place  he  has 
considerable  leverage  to  help  him  and  the  moment  the  valve  is 
opened  a  hair's  breadth  the  valve  is  in  equilibrium.  In  the 


O 


B     \ 


FIG.  62.— Throttle  valve. 


182  THE   RAILWAY  LOCOMOTIVE 

second  place,  the  rod,  where  it  passes  through  the  stuffing  box 
before  referred  to,  is  more  than  an  inch  diameter.  If  it  has  a 
square  inch  of  sectional  area  then  the  steam  pressure  inside  the 
boiler  will  tend  to  push  the  rod  out,  so  assisting  the  driver  with 
an  effort  of  200  Ibs.  By  making  the  rod  still  larger  we  can  go 
on  restoring,  so  to  speak,  equilibrium.  But  it  must  be  kept  in 
mind  that  the  resistance  to  opening  the  valve  only  exists  so  long 
as  it  is  shut ;  as  soon  as  it  is  opened  at  all  the  pressure  inside  and 
outside  the  valve  box  becomes  nearly  the  same.  The  thrust  on 
the  rod  is  then  unbalanced,  and  the  valve  as  soon  as  opened  a 
little  would  be  forcibly  lifted  as  far  as  it  would  go.  To  prevent 
this  the  lever  on  the  back  of  the  fire-box  works  in  an  arc,  known 
in  the  United  States  as  a  "  gate  "  ;  this  is  provided  with  notches 
into  which  drops  a  detent  working  on  the  edge  of  the  regulator 
lever.  In  this  way,  the  valve  may  be  set  open  much  or  little. 
Sometimes  the  lever  is  fitted  with  a  fly  nut,  by  which  it  may  be 
secured  in  any  position. 

In  some  cases  the  bell  crank  is  so  set  that  the  regulator  handle 
has  a  very  greatly  augmented  leverage  at  first,  so  that  the 
valve  can  be  opened  by  a  small  effort  just  enough  to  admit 
steam  to  the  engine  and  so  establish  equilibrium. 

In  this  country  the  double -beat  valve  is  little  used,  the  sliding 
valve  being  preferred.  The  main  steam  pipe  is  fitted  with  an 
elbow  rising  into  the  dome.  The  mouth  of  the  pipe  is  stopped 
by  a  vertical  plate,  in  which  are  two  or  more  rectangular  holes  or 
ports;  on  this  plate  slides  another  with  similar  holes.  When 
the  holes  coincide,  steam  is  admitted  to  the  cylinders.  The  plate 
can  be  moved  up  arid  down  in  either  of  two  ways.  According  to 
the  first,  a  bell  crank  and  rod  are  fitted  precisely  as  just  described. 
The  horizontal  limb  of  the  bell  crank  then  moves  the  sliding 
plate  up  and  down.  More  usually  a  "  winch  "  handle  is  used, 
and  an  arm  on  the  long  spindle  is  jointed  just  under  the  dome  to 
the  valve.  A  partial  revolution  of  the  regulator  handle  then 
suffices  to  put  on  or  shut  off  steam  in  a  way  with  which  every 
one  who  has  seen  a  locomotive  started  is  familiar.  In  all  this 
there  is  little  room  for  variety.  One  improvement  may  be 
mentioned  in  the  valve.  It  consists  in  placing  a  subsidiary 


BOILER  FITTINGS  183 

sliding  plate  on  the  back  of  the  principal  valve,  which  plate  has 
a  small  hole  in  it.  When  steam  is  shut  off,  there  is,  of  course,  a 
heavy  pressure  on  the  back  of  the  sliding  valve  which  makes  it 
hard  to  open  the  regulator.  Now  the  first  effect  of  moving  the 
regulator  handle  is  to  act  on  the  subsidiary  valve,  which  offers 
little  resistance.  This  admits  steam  at  once  to  the  main  steam 
pipe  between  the  cylinders  and  the  regulator.  This  equalises 
the  pressure  on  both  sides  of  the  larger  plate,  which  can  then 
move  quite  freely.  On  the  London  and  South  Western  Kailway, 
Mr.  Drummond  has  entirely  done  away  with  the  stuffing  box. 
A  collar  on  the  regulator  spindle  has  a  face  ground  to  fit  the 
inner  end  of  the  brass  casting  through  which  the  spindle  passes. 
The  pressure  of  the  steam  thrusts 
the  collar  against  the  casting, 
making  a  steam-tight  joint. 

Safety  valves  are  important, 
although  good  firemen  seldom 
give  them  much  work  to  do. 
They  do  not  require  minute 
description.  The  first  safety  valves  were  always  loaded  directly  by 
a  lever  of  the  second  order.  They  were,  as  they  are  still,  conical 
brass  or  gunmetal  valves  resting  on  seats  of  the  same  metal.  They 
constituted  ornamental  features,  being  carried  on  fluted  columns, 
standing  a  couple  of  feet  above  the  top  of  the  boiler.  The  load- 
ing was  always  effected  by  a  spring  balance  as  shown  in  Fig.  63, 
and  the  area  of  the  valve,  the  length  of  the  lever,  and  the 
graduation  of  the  spring  balance  index  were  so  adjusted  to  each 
other  that  the  figures  on  the  index  plate  B  showed  the  pressure 
when  the  valve  blew  off.  Now,  the  index  hand  was  carried  by  a 
stout  stud,  and  it  was  quite  possible  by  turning  the  adjusting 
nut  by  which  the  pressure  at  which  the  valve  lifted  was  regulated, 
to  set  the  stud  hard  against  the  top  of  the  slot  in  which  it  moved. 
Then  the  valve  could  not  lift  at  all.  Engine  drivers  with  trains 
a  little  too  heavy  were  in  the  habit  of  so  setting  safety  valves  fast 
in  order  to  get  more  pressure.  Even  when  an  explosion  did  not 
follow,  the  boilers  were  strained  and  the  tubes  caused  to  leak. 
Ferrules,  as  at  A  in  dotted  lines,  were  then  fitted  on  the  screws 


184 


THE  KAIL  WAY  LOCOMOTIVE 


of  the  spring  balances,  so  that  they  could  no  longer  have  the 
indexes  set  up  against  the  tops  of  the  slots.  Then  the  engine- 
men  loaded  the  lever  direct  with  anything,  such  as  a  couple  of 
links  of  wagon  chain.  To  meet  this,  Mr.  Eamsbottom,  when 
Locomotive  Superintendent  of  the  London  and  North  Western 
Eailway  many  years  ago,  invented  a  most  ingenious  valve, 
which  is  largely  used  now,  and  was  used  to  the  almost  total 
exclusion  of  all  other  valves  up  to  a  recent  period.  It  is  illus- 
trated in  Fig.  64.  Two  valves  of  precisely  the  same  size  are 
placed  side  by  side  on  top  of  short  pillars ;  between  them  is  a 
stout  coiled  spring,  one  end  of  which  is  hooked  into  an  eye 
between  the  two  pillars,  and  the  other  into  a  hole  in  the  middle 

of  a  lever.  Projections  or  horns 
on  the  lever  bear  on  the  centres 
of  the  two  conical  valves.  It 
will  be  understood  in  a  moment 
that  the  one  spring  loads  both 
the  valves,  and  must  be  twice  as 
strong  as  if  it  loaded  only  one. 
A  diameter  of  a  little  over  three 
inches,  with  an  area  of  ten 
inches,  is  a  very  common  size 
for  a  safety  valve.  If  the  pressure  is  150  Ibs.  then  each  valve 
must  be  held  down  under  a  force  of  150  X  10  =  1,500  Ibs.  or  for 
the  two  valves,  3,000  Ibs.,  and  the  spring  must  be  strong  enough 
to  apply  this  pressure.  The  end  of  the  lever  is  prolonged  into 
the  cab,  and  the  driver  can  always  be  certain  that  a  valve  is  not 
sticking,  because  by  pulling  down  the  end  of  the  lever  he  takes 
all  the  load  off  the  valve  furthest  from  him,  and  by  lifting  it  up 
all  the  load  off  the  valve  next  to  him. 

At  first  sight  it  would  appear  that  this  valve  could  not  be  over- 
loaded, as  the  load  was  settled  for  good  in  the  workshops  by 
adjusting  the  lengths  of  the  horns  on  the  lever.  But,  even  so, 
the  enginemen  were  not  beaten.  They  overloaded  the  valves 
by  putting  shot  into  the  excavation  in  the  tops  of  the  valves. 
When  there  was  no  steam  in  the  boiler,  by  pulling  down  the  lever 
they  lifted  the  horn  on  the  outer  valve  and  the  shot  ran  in  under 


Boiler 
FIG.  64. 


BOILER  FITTINGS  185 

it.  The  same  process  produced  a  like  result  with  the  other  valve. 
The  effect  was  the  same  as  lengthening  the  horns ;  the  tension 
of  the  spring  was  increased,  and  in  this  way  10  Ibs.  or  20  Ibs. 
were  added  to  the  pressure.  All  loose  shot  was  carefully  removed, 
and  until  the  valves  came  to  be  specially  examined  the  fraud 
was  never  detected.  Mr.  Webb,  Mr.  Eamsbottom's  successor, 
then  fitted  the  valves  with  a  casing  so  constructed  that  shot 
could  not  be  put  into  the  valves,  and  he  offered  a  reward  of  ^5 
to  any  man  who  could  overload  the  valves  ;  the  money  was 
never  claimed. 

"Within  the  last  few  years  it  has  been  deemed  desirable  to  fit 
more  than  two  safety  valves  to  the  very  large  boilers  now  in  use, 
and  something  more  compact  than  the  Kamsbottom  valve 
became  desirable.  Therefore,  we  now  find  three  or  even  four 
valves  loaded  direct,  each  by  a  coiled  spring,  and  grouped  in  one 
casing.  No  easing  gear  is  needed,  because  the  valves  are 
constantly  under  observation,  and  it  is  almost  impossible  that 
they  should  all  stick.  On  some  lines  "  Pop  "  valves  have  been 
tried.  They  are  so  called,  because  instead  of  rising  gradually  as 
the  pressure  increases  after  they  have  begun  to  blow  off,  they  lift 
suddenly  with  a  "  pop  "  and  blow  off  hard  for  a  minute  or  so  until 
they  have  reduced  the  pressure  about  3  Ibs.,  then  they  shut 
suddenly  until  the  pressure  again  rises,  and  so  on.  This  inter- 
mittent action  is  very  noisy  and  objectionable  in  railway  stations. 
It  alarms  passengers,  and  does  no  good,  so  pop  valves  have  never 
found  much  favour  with  locomotive  superintendents.  The  pop 
action  is  got  by  so  shaping  the  valve  and  valve  seat  that  the  area 
on  which  the  steam  can  act  is  augmented  by  the  rising  of  the 
valve. 

It  is  essential  that  the  precise  level  at  which  the  water  stands 
in  the  boiler  should  be  known.  In  old  times — and  indeed,  to  this 
day  in  America — three  "  pet  "  cocks,  or  "  try  "  cocks,  were  screwed 
into  the  back  of  the  fire-box  about  3  inches  above  each  other.  If 
when  the  lower  one  was  opened  steam  came  out,  then  the  water 
was  too  low.  If  when  the  top  one  was  tried  water  came  out,  it 
was  too  high  ;  when  it  was  just  right,  steam  came  out  of  the 
top  cock,  water  and  steam  out  of  the  middle  cock,  and  water  alone 


180  THE  KAIL  WAY   LOCOMOTIVE 

out  of  the  lower  cock.  The  indications  thus  supplied  were  not 
easy  to  read,  because  the  hot  water  flashed  into  steam  at  once. 
The  whole  system  was  dirty  and  inefficient,  and  has  long  since 
been  superseded  by  the  glass  water  gauge,  which  is  too  familiar 
to  require  illustrations.  The  tube  is  made  of  a  very  special  hard 
glass  with  a  minimum  of  alkali  in  it,  which  will  not  dissolve 
under  the  high  pressure  to  which  it  is  exposed.  Soft  glass  in  high 
pressure  steam  will  become  cloudy  and  corroded  in  a  few  hours. 
The  glass  tube  is  passed  through  a  stuffing  box  at  each  end,  in 
which  it  is  packed  by  india-rubber  rings,  which  permit  free  move- 
ment. Any  attempt  to  confine  the  tube  is  certain  to  result  in 
breakage.  It  is  usually  about  half-an-inch  bore.  Since  very 
high  pressures  have  been  introduced,  it  is  usual  to  box  the  gauge 
up  in  a  shield  made  of  pieces  of  thick  plate  glass,  because  a 
broken  gauge  tube  is  apt  to  fly  and  wound  the  driver  or  fireman. 
In  some  cases  gauges  are  fitted  with  ball  valves  at  the  top  and 
bottom,  which  remain  at  rest  in  little  pockets  unless  the  glass 
gives  way.  Then  the  violent  rush  of  steam  above  and  water 
below  lifts  the  balls,  and  blowing  them  on  to  seats,  the  steam  and 
water  are  automatically  shut  off.  When  the  driver  shuts  the 
stop  cocks  the  automatic  valves  fall  away  again  to  their  normal 
position. 

We  have  now  got  the  boiler  complete,  with  all  the  appur- 
tenances which  concern  the  outflow  of  steam  from  it  except  the 
whistle,  which  does  not  require  description ;  and  we  have,  lastly, 
to  consider  the  means  by  which  water  is  put  into  it. 


CHAPTER   XXV 

THE    INJECTOll 

A  LOCOMOTIVE  will  evaporate,  according  to  its  size  and  its  load, 
from  three  to  seven  tons  of  water  per  hour,  and  as  this  has  to  be 
forced  into  the  boiler  with  certainty  and  regularity  just  as  it  is 
wanted,  it  will  be  seen  that  the  efficiency  of  the  feeding  apparatus 
is  of  the  last  importance.  For  many  years  the  water  was  invari- 
ably pumped  in.  Two  horizontal  plunger  force  pumps  were  fixed 
inside  the  frames,  one  at  each  side,  the  plungers  being  moved  by 
the  cross  heads  on  the  piston  rods.  Now  and  then  short-stroke 
pumps,  worked  off  the  crank  shaft  by  eccentrics,  were  used.  The 
steam  locomotives  on  the  Metropolitan  and  District  Kail  ways  were 
thus  fed.  No  recently  built  engines,  however,  are  fitted  with  feed 
pumps  save  under  special  circumstances,  and  it  is  unnecessary  to 
say  more  about  them  than  that  they  presented  no  particular  features 
of  any  kind  calling  for  description.  The  system  was  inconvenient 
because  no  water  could  be  put  into  the  boiler  while  the  engine 
was  standing.  It  was  not  at  all  unusual  to  have  to  uncouple  a 
locomotive  from  its  train,  and  run  it  up  and  down  the  line  for 
half  a  mile,  both  pumps  going  for  all  they  were  worth,  until  the 
boiler  was  replenished,  and  then  couple  it  up  again  to  its  train. 
A  simpler  plan  was  to  jam  the  brakes  hard  on  the  tender  wheels, 
then  to  oil  the  rails  and  the  rims  of  the  driving  wheels,  which  of 
course  were  not  coupled,  and  then  to  turn  on  steam  and  let  the 
driving  wheels  revolve,  both  pumps  being  at  work.  When  the 
boiler  was  satisfied  the  brakes  were  taken  off,  and  a  couple  of 
shovelsful  of  sand  on  the  rails  enabled  the  engine  to  move  ahead. 
Later,  engines  were  often  fitted  with  small  donkey  feed  pumps. 

Locomotive  boilers  in  the  present  day  are  always  fed  by  injec- 
tors. The  injector  is  an  instrument  so  remarkable  and  so 


188  THE  EAILWAY  LOCOMOTIVE 

paradoxical  in  its  action  that  it  cannot  be  dismissed  in  a  few 
words.  It  has  been  made  the  subject  of  much  mathematical 
investigation,  to  which  it  lends  itself  so  badly  that  no  satisfactory 
theory  has  been  established  which  will  account  for  all  the 
phenomena  which  it  presents.  Enough  is  however  known  to 
enable  an  entirely  adequate  explanation  of  its  action  to  be  given. 

A  comparatively  small  quantity  of  steam  supplied  by  the  boiler 
is  passed  through  the  injector  and  picks  up  cold  water  from  the 
tender,  heats  it,  and  forces  it  into  the  boiler.  The  paradox  is 
that  steam  of,  say,  150  Ibs.  pressure  should  come  out  of  the  boiler, 
and  then  find  its  way  in  again,  carrying  the  feed  water  with  it, 
against  the  same  150  Ibs.  pressure.  Here  we  apparently  eat  our 
cake  and  still  have  it.  It  is  not  remarkable  that  on  its  lirst  intro- 
duction engineers  refused  to  believe  in  it.  Articles  indeed  were 
written  to  prove  that  all  the  laws  of  the  conservation  of  energy 
would  have  to  be  remodelled  if  the  injector  really  worked,  and 
much  more  to  the  same  effect.  The  injector  works,  however, 
and  no  one  now  thinks  that  it  upsets  any  law.  On  the  contrary, 
it  is  a  beautiful  embodiment  of  laws  lying  at  the  root  of  all 
thermodynamical  facts. 

How  the  injector  came  into  existence  is  not  accurately  known. 
It  originated  with  M.  Henri  Giffard,  a  French  engineer,  in 
1858.  So  far  as  available  information  goes  it  was  a  discovery, 
not  an  invention.  He  brought  it  over  to  this  country,  and 
Messrs.  Sharp,  Stewart  &  Company,  very  eminent  locomotive 
engine  builders  of  Manchester,  acquired  the  sole  rights,  and  for 
many  years  constantly  effected  improvements.  The  expiration 
of  the  original  patents  threw  the  injector  open  to  the  world. 
Several  firms  took  up  its  manufacture,  and  it  is  to-day  a  very 
different  instrument  from  what  it  was  originally.  The  first 
locomotive  in  this  country  to  be  fitted  with  an  injector  was  the 
"  Problem,"  an  engine  with  outside  cylinders  and  a  single  pair  of 
driving  wheels,  7  feet  6  inches  in  diameter.  Sixty  of  these 
engines  were  built  by  Mr.  Eamsbottom  at  Ore  we  for  the  Northern 
(Holyhead  and  Crewe)  section  of  the  London  and  North  Western 
Eailway  in  1862. 

When  a  jet  of  steam  is  permitted  to  strike  against  an  obstacle 


THE   INJECTOR  189 

it  loses  its  velocity,  and  its  momentum  reappears  as  pressure. 
It  is  only  necessary  to  hold  a  board  in  front  of  a  jet  of  steam  to 
prove  this.1 

Let  us  suppose  that  a  bullet-proof  plate  is  supported  by  a 
spring  at  the  back,  and  that  a  rifle  is  fired  at  it.  The  plate 
will  be  driven  back  and  move  forward  again  every  time  it  is 
struck. 

Let  us  now  further  suppose  that  instead  of  a  single  rifle  the 
plate  is  fired  at  by  small  machine  guns ;  the  bullets  will  now 
impinge  on  the  plate  so  rapidly  that  it  will  not  move  forward  at 
all.  The  spring  will  be  kept  permanently  compressed,  and  we 
shall  have  to  all  intents  and  purposes  the  momenta  of  the  bullets 
converted  into  pressure.  Now  the  molecules  of  steam,  however 
small  they  are,  possess  momentum,  and  so,  as  has  been  said, 
they,  acting  as  so  many  tiny  bullets,  produce  pressure  on  any 
surface  against  which  they  strike. 

The  force  with  which  each  bullet  strikes  is  expressed  by  the 

M  V2 
equation  E  =  -grq    where  E  is  the  stored-up  energy  in  the  bullet, 

M  its  mass  and  V2  the  square  of  its  velocity.  The  meaning  of 
this  is  that  if  a  bullet  had  a  velocity  of  1,000  feet  per  second,  and 
weighed  one-tenth  of  a  pound,  then  at  the  moment  of  striking  it 
represented  energy  sufficient  to  lift  1,537  Ibs.  a  foot  high,  or 
18,444  Ibs.  one  inch  high,  or  184,440  Ibs.  one-tenth  of  an  inch, 
and  so  on.  The  fact  with  which  we  have  to  deal  is  that  energy 
augments,  not  as  the  velocity,  but  as  the  square  of  the  velocity. 
Next  let  us  suppose  that  two  bullets  of  equal  weight  moving  at 
the  same  velocity  in  opposite  directions  encounter  each  other. 
It  is  clear  that  they  would  be  flattened  or  shattered.  Neither 
would  give  way  and  retire  before  the  other.  If,  however,  one  of 
the  bullets  moved  faster  than  the  other,  then  the  slower  bullet 
would  be  overcome,  and  we  may  then  suppose  the  two  bullets 

1  The  accepted  theory  explaining  why  gases  exert  pressure  on  the  inside 
of  the  vessel  containing  them  is  that  the  molecules  of  which  the  gas  consists 
are  in  extremely  rapid  motion,  continually  striking  against  and  rebounding 
from  the  wall,  just  as  a  billiard  ball  rebounds  from  the  cushions.  The 
number  is  so  enormous  that  individual  impacts  cannot  be  distinguished,  and 
the  average  effect  is  to  produce  pressure. 


190  THE  RAILWAY  LOCOMOTIVE 

moving  together  at  a  less  speed  than  either  possessed  before, 
in  the  direction  of  the  flight  of  the  hullet  with  the  greatest 
velocity. 

To  put  this  in  another  way,  let  us  suppose  that  a  jet  of  steam 
is  suddenly  turned  into  a  swarm  of  hailstones.  If  the  steam  was 
moving  at,  say,  3,000  feet  per  second,  it  is  clear  that  the  hail 
would  continue  to  move  at  just  the  same  velocity.1  In  the  same 
way,  if  the  steam  were  turned  into  water,  the  velocity  of  the  water 
would  be  that  of  the  steam,  and  if  the  water  was  turned  into 
another  body  of  water  it  is  clear  once  more  that  it  would  set  up  a 
violent  current  in  that  water. 

So  far  nothing  has  been  said  about  getting  water  into  the 
boiler.  Let  us  suppose,  however,  that  our  jet  of  steam,  on  its 
way  to  the  nozzle  through  which  it  flows,  comes  in  contact  with 
cold  water.  The  result  will  be  that  it  will  be  condensed,  but,  as 
has  just  been  shown,  it  will  not  thereby  cease  its  onward  flight. 
It  will  transfer  its  momentum  to  some  of  the  cold  water,  which 
will  then  join  the  condensed  steam,  and  by  dint  of  sheer 
'momentum  the  two  will  force  their  way  into  the  boiler.  The 
steam  will  play  the  part  of  gunpowder,  and  the  water  will  act  as 
a  bullet,  producing,  as  we  have  explained  for  machine-gun  bullets, 
a  pressure  which  suffices  to  overcome  the  resistance  offered  by 
the  water  under  pressure  in  the  boiler,  and  so  the  boiler  is 
supplied,  and  water  thus  propelled  will  enter  a  steam  space  just 
as  freely  as  it  will  a  water  space.  All  this  is  so  far  sufficiently 
simple  and  obvious;  but  the  discovery  of  a  principle  and  the 
putting  of  that  principle  into  practice  are  t\vo  very  different 
things. 

The  first  injectors  made  were  very  uncertain  in  their  action, 
very  large,  and  required  many  adjustments  to  induce  them  to 
start  and  to  keep  them  going.  These  troubles  have  been  got 
over  in  large  part  by  the  introduction  of  what  is  known  as  the 
diverging  nozzle,  and  in  part  by  the  use  of  very  simple  and  yet 

1  This  is  not  strictly  correct  because  of  the  reduction  in  volume,  but  the 
inaccuracy  is  of  no  consequence  here.  The  reader  is  referred  to  any  good 
text  book  of  physics  for  the  mathematics  of  the  flow  of  gases  and  liquids  under 
varying  conditions. 


THE  INJECTOE 


191 


very  efficient  automatic  self-adjusting  devices  which  do  what  the 
fireman  had  to  do  at  first  but  very  much  better.  The  theory  of 
the  diverging  nozzle  is  set  forth  with  much  prominence  in  most 
treatises  on  hydraulics  and  all  treatises  on  steam  turbines,  to 
which  the  reader  who  desires  further  information  is  referred. 
For  our  present  purpose,  it  is  enough  to  say  that  it  gives  a  more 
powerful  and  compact  jet  than  can  be  had  without  it.  The 
accompanying  engraving,  Fig.  65,  shows  an  injector  as  used  on 
locomotives  thirty  years  ago,  and  one  quite  efficient  and  able  to 
work.  The  steam  enters  at  A  and  passes  through  the  diverging 


FIG.  65. — Section  of  injector. 

cone  B.  Through  C  cold  water  from  the  tender  enters.  D  is  a 
cock  for  regulating  the  supply.  In  dealing  with  draught  it  has 
been  shown  that  the  exhaust  steam  drawTs  the  products  of  com- 
bustion with  it  and  sends  them  up  the  chimney.  Now  in  just 
the  same  way  the  steam  leaving  A  draws  in  water,  is  condensed, 
and  drives  it  forward  through  the  second  nozzle,  which  is  con- 
tracted because  the  steam  being  rapidly  condensed  the  volume 
to  be  passed  through  E  is  much  diminished.  The  condensed 
steam  and  feed  water  leap  across  the  gap  F  and  enter  the  cone  E, 
which  it  will  be  seen  is  an  expanding  nozzle  at  the  end  of  which 
is  a  check  valve  G,  intended  to  prevent  the  return  of  water  from 
the  boiler  when  the  injector  is  stopped.  E  is  expanded  in  order 


192  THE   RAILWAY  LOCOMOTIVE 

that  the  velocity  of  the  steam  may  be  reduced  and  its  "  energy  of 
translation  "  converted  into  pressure.  B  and  E  are  united  by 
two  bridges  in  a  way  that  will  be  understood  from  the  cross  section 
of  the  overflow  cock  H. 

It  may  be  asked,  Why  not  make  the  two  cones  B  and  E  con- 
tinuous ?  The  answer  is  that  the  injector  will  not  always  start. 
The  water  is  indeed  driven  into  E,  but  not  with  force  enough  to 
get  into  the  boiler.  Usually  this  is  because  too  much  water  gets 
in  at  C  and  drowns  the  instrument.  To  provide  for  this,  the 
overflow  cock  H  is  fitted,  through  which  the  surplus  water 
escapes  until  the  supply  of  water  has  been  exactly  adjusted  to 
the  steam.  It  may  be  that  only  the  proper  quantity  of  water 
goes  in,  but  there  is  too  much  or  too  little  steam.  When  all  the 
proper  adjustments  are  made,  the  injector  sings,  and  the  only 
loss  of  water  is  represented  by  a  few  drops  which  escape  now  and 
then  at  H. 

The  injector  illustrated  will  not  lift  cold  water,  because  it  cannot 
make  a  sufficient  vacuum  in  C.  The  difficulty  is  got  over  by  the 
simple  expedient  of  reducing  the  diameter  of  the  steam  nozzle, 
so  that  it  is  smaller  than  the  discharge  cone  E.  This  was 
formerly  effected  by  putting  a  conical  spindle  into  A.  Once  the 
injector  was  started,  the  cone  was  gradually  withdrawn  to  permit 
the  entrance  of  sufficient  steam. 

A  defect  in  all  the  earlier  forms  of  injectors  was  that  they  were 
liable  to  be  thrown  off  by  jerks,  which  caused  the  water  to  surge 
in  the  tender,  or  in  the  feed  pipes  or  boiler.  When  this  happened, 
the  fireman  had  to  make  all  the  adjustments  over  again,  which 
was  not  an  easy  task  on  a  jumping  footplate.  Accordingly 
various  inventors  sought  a  remedy,  and  now  all  injectors  on 
locomotives  are  of  the  self -starting  self-adjusting  type.  The 
modern  injector  is  not  very  much  larger  than  a  champagne 
magnum,  and  requires  no  attention  of  any  kind.  To  start  it,  the 
fireman  has  only  two  handles  to  turn,  one  on  the  tender  which 
lets  water  into  the  injector,  and  the  other  on  the  back  of  the 
fire-box,  which  admits  steam.  Two  injectors  are  always  fitted. 
It  is  a  usual  though  not  an  invariable  practice  to  make  one  of 
these  very  nearly  but  not  quite  sufficient  to  keep  the  boiler 


THE  INJECTOR 


193 


supplied.  At  the  beginning  of  a  run  it  is  started,  and  is  not 
meddled  with  while  the  train  is  running.  The  rest  of  the  feed 
is  put  in  by  the  other  injector,  which  is  used  or  disused  by  the 
fireman  according  to  the  rate  at  which  evaporation  goes  on  in 
the  boiler. 

It  may  be  asked  what  effect  the  temperature  of  the  feed  water 
has  on  the  instrument.  The  answer  is  that  unless  it  is  cold 
enough  to  condense  the  steam,  the  injector  will  not  work. 
The  critical  temperature  for  ordinary  injectors  is  about  120°  F. 
At  this  temperature  the  quantity  of  water  injected  is  about 
20  per  cent,  less  than  at  50°  F.  The  higher  the  boiler  pressure, 
the  colder  must  be  the  feed  water.  As  to  the  actual  amounts 
fed,  the  makers  of  injectors  guarantee  those  set  forth  in  the 
following  table :— 


Boiler  Pressure. 

Ibs.  of  Water  delivered 
per  Ib.  of  Steam. 

60  Ibs. 

19 

90    „ 

16 

120    „ 

14 

200    ,, 

10 

It  is  not  necessary  to  describe  in  detail  the  construction  of  a 
number  of  the  injectors  used  on  locomotives.  There  are  a  great 
many  by  different  makers.  Sufficient  has  been  said  to  give  the 
reader  an  adequate  idea  of  the  theory  of  this  very  curious 
instrument,  a  theory,  it  may  be  added,  which  is  neither  so 
complete  nor  so  sound  as  is  desirable.  All  that  the  injector 
has  to  do  is  to  overcome  the  static  head  of  the  water  or  of 
the  steam  which  is  measured  by  the  pressure  on  the  boiler 
side  of  the  check  valve.  In  effect  there  is  a  close  analogy 
between  the  hydraulic  ram  and  the  injector.  The  necessary 
momentum  being  obtained  not  from  gravity  but  from  the 
impulse  supplied  by  the  steam. 

R.L.  o 


194 


THE  RAILWAY  LOCOMOTIVE 


Any  account  of  the  injector  would  be  incomplete  unless  it 
took  account  of  the  recent  modifications  which  have  made  the 
instrument  self -star  ting.  One  example,  an  injector  made  recently 


Right:  Hand  Injector  made 
without:  Overflow  cock 


Overflow 

\ 
PIG.  66. — Self -starting  injector. 


for  locomotives  by  Messrs.  Gresham  &  Craven  of  Manchester, 
is  illustrated  by  Fig.  66. 

Let  it  be  remembered  that  the  action  of  an  injector  depends 
upon  the  fact  that  the  velocity  of  a  jet  of  steam  discharging  into 
the  combining  tube  is  twenty  to  twenty-five  times  that  of  a  jet  of 
water  issuing  from  a  boiler  under  the  same  pressure,  and  that 
the  enormous  reduction  of  the  volume  of  the  steam,  during 


THE  INJECTOR  195 

condensation  by  the  water,  concentrates  the  momentum  of  the 
jet  upon  the  area  of  the  delivery  tube,  which  is  but  a  small 
fractional  part  of  the  orifice  from  which  it  issues,  leaving  a 
large  margin  of  available  energy. 

This  action  has  been  ingeniously  likened  to  a  pump  with  a 
continuous  piston  equal  to  the  area  of  the  steam  nozzle  forcing 
a  continuous  ram  equal  to  the  lesser  area  of  the  delivery  throat, 
the  ram  in  this  case  being  a  small  bar  of  "  solid  "  water.1 

The  cones  in  the  Gresham  injector  are  made  in  four  parts, 
viz. : — No.  1,  Steam  Cone  ;  No.  2,  Lifting  Cone  ;  No.  3,  Combining 
Cone  ;  No.  4,  Delivery  Cone. 

An  internal  steam  pipe  from  the  dome  of  the  locomotive 
conveys  steam  to  the  injector  steam  valve  A,  which  upon  being 
opened  admits  steam  to  the  steam  nozzle  1  by  the  passage  B. 
The  steam  issuing  from  the  steam  nozzle  lifts  the  base  of  the 
combining  cone  3,  which  is  free  to  slide  in  its  guide,  off  its 
seat,  and  passes  out  freely  through  this  opening  to  the  overflow 
passage  C,  and  on  to  the  pipe  of  the  injector.  In  so  doing,  it 
creates  a  partial  vacuum  in  the  water  pipe  D,  and  the  water 
rises  to  the  injector.  The  water  coming  in  contact  with  the 
steam,  travels  with  it  through  the  lifting  cone  2,  and  gradually 
condenses  it. 

The  velocity  of  the  steam  being  now,  as  previously  explained, 
largely  transferred  to  the  water,  the  latter  passes  from  the 
lifting  cone  2,  and  through  the  combining  cone  3  (which  is  now 
drawn  back  on  to  its  face  at  E,  owing  to  the  high  vacuum 
created  in  the  chamber  F  by  the  passage  of  the  jet),  and  these 
two  cones,  2  and  3,  become  one  combining  cone,  i.e.,  the  cone 
in  which  the  steam  and  water  combine.  After  passing  through 
this  combining  cone  the  jet  flows  out  at  the  overflow  space  G 
and  down  the  passage  and  overflow  pipe  C  until  such  time  as 
it  attains  sufficient  velocity  to  carry  itself  past  this  space  and 

1  The  word  "solid"  is  not  out  of  place.  Dr.  Le  Bon,  the  great  French 
physicist,  cites  the  case  of  a  jet  of  water  used  to  drive  a  Pelton  wheel. 
The  head  is  1,600  feet.  The  jet  is  1  inch  in  diameter.  It  is  absolutely 
impossible  for  the  strongest  man  to  cut  through  this  jet  with  a  sword,  but 
the  sword  can  be  broken  in  the  attempt. 

o2 


196  THE  RAILWAY   LOCOMOTIVE 

enter  the  delivery  cone  4.  When  it  reaches  this  point  its 
velocity  is  so  great  that  it  is  sufficiently  powerful  to  pass  by  the 
passage  H,  and  lift  the  back  pressure  valve  1,  and  so  enter  the 
boiler. 

The  boilers  of  locomotives  are  invariably  carefully  clothed  or 
"lagged"  for  three  reasons.  First  to  prevent  the  radiation  of 
heat,  secondly  for  protection  from  the  weather,  and  lastly  for 
the  sake  of  appearance.  The  earliest  engines  were  "rattle- 
boarded,"  the  lagging  consisted  of  narrow  strips  of  wood  beaded, 
and  tongued  with  hoop  iron,  secured  round  the  boiler  with  hoops, 
very  often  of  brass  kept  polished.  The  fire-boxes  of  Bury's 
engines,  which  were  semicircular  in  plan,  were  carried  up  in  the 
shape  of  domes  to  give  steam  room,  and  covered  with  copper. 
Hence  the  name  of  "  copper  nob  "  which  they  obtained  in  the 
north.  In  France,  while  the  boards  were  retained,  they  were 
covered  with  thin  sheet  iron,  and  in  some  cases  in  passenger 
engines  with  brass  sheets,  which  were  kept  bright.  This  was 
all  very  well  while  coke  was  the  fuel,  when  coal  came  in  brass 
went  out.  Subsequently  felt  was  interposed  between  the  boards 
and  the  boiler,  and  the  whole  covered  with  Eussia  iron.  When 
pressure  rose  the  system  would  not  answer,  the  felt  was  scorched 
and  the  boards  caught  fire.  In  the  present  day  the  lagging 
generally  consists  of  some  preparation  of  asbestos,  often  put  on 
in  the  form  of  mattresses,  and  covered  outside  with  sheet-steel 
plates.  Abroad  these  plates  are  often  left  without  paint,  their 
natural  oxide  coating  serving  with  the  aid  of  a  little  oil  to 
prevent  rust.  In  this  country  they  are  always  heavily  painted 
and  varnished,  each  railway  having  its  distinguishing  colours. 
The  cost  of  painting  and  varnishing  is  a  heavy  item.  It  has  been 
stated  that  Mr.  Samuel  Johnson  saved  the  Midland  Company 
several  thousand  pounds  a  year  by  substituting  red  oxide  of  iron 
for  more  expensive  pigments.  This  is  the  reason  why  Midland 
engines  are  dull  red.  Mr.  Webb  used  black  on  the  London  and 
North  Western,  relieved  in  the  case  of  passenger  trains  by 
lining.  The  goods  and  coal  engines  he  kept  all  black,  and  they 
were  called  by  the  profane  "  Webb's  flying  hearses." 

The  loss  by  radiation  from  an  unclothed  boiler  is  considerable 


THE  INJECTOE  197 

and  with  efficient  lagging  not  great.     Professor  Goss  gives  the 
following  table : — 

Power  lost  by  Radiation.  Horse  power. 

Bare  boiler  at  rest        12 

,,         ,,     running  at  28  miles  an  hour     25 

Covered  boiler  at  rest  ...         ...         ...         ...         ...  4*5 

,,  ,,       running  at  28  miles  an  hour  ...         9*3 

Much  depends  on  the  external  temperature.  The  maximum 
possible  loss  for  an  un lagged  boiler  seems  to  be  about  10  per 
cent.,  and  for  a  clothed  boiler  4  per  cent. 


SECTION  III 

THE  LOCOMOTIVE  AS  A  STEAM  ENGINE 
CHAPTEE  XXVI 

CYLINDERS    AND    VALVES 

IN  all  that  concerns  the  work  done  by  the  engines  of  a  loco- 
motive they  may  be  treated  precisely  as  though  they  were 
stationary  engines  on  land.  By  "work  done"  must  be  under- 
stood the  development  of  power.  The  effect  produced  on  the 
locomotive  as  a  vehicle  has  already  been  mentioned ;  it  will 
be  dealt  with  again  further  on.  The  thermodynamic  laws  ;  the 
heat  exchanges  ;  the  effects  of  expansion,  compression  and  wire 
drawing,  are  just  the  same  for  the  engines  of  a  locomotive  that 
they  are  for  a  stationary  or  marine  engine  working  without 
a  condenser.  The  engines  do  not  know  that  they  are  travelling 
through  space  at  high  velocities,  instead  of  working  on  fixed 
frame  plates  in  a  factory.  The  principal  difference,  indeed, 
between  them  and  stationary  engines  is  that  the  latter  as  a 
rule  can  run  in  only  one  direction,  while  the  engines  of  a 
locomotive  must  be  capable  of  turning  round  equally  well  in 
either  direction.  In  this  respect  they  resemble  a  marine 
engine ;  the  fact  complicates  the  valve  gear,  as  will  be  explained 
further  on. 

Locomotives  are  always  propelled  by  the  action  of  steam 
pressing  on  pistons  reciprocating  in  cylinders,  which  pistons 
cause  the  revolution  of  an  axle  by  means  of  cranks  and  connect- 
ing rods.  There  are  no  locomotives  in  existence  propelled  by 
rotary  engines  or  turbines.  Up  to  a  comparatively  recent  period 


CYLINDEES  AND  YALVES  199 

locomotives  were  divided  into  two  classes  only — inside  and 
outside  cylinder.  Subdivisions  are  now  necessary,  because 
locomotives  are  made  with  both  in  combination.  In  this  country 
although  outside  cylinders  are  freely  used,  inside  cylinders  have 
always  been  preferred.  In  the  United  States  on  the  contrary 
the  outside  cylinder  has  been  so  favoured  that  very  few  inside 
cylinder  engines  have  been  built. 

Although  in  the  present  day  the  construction  and  mode  of 
action  of  a  simple  steam  engine  are  very  generally  understood,  it 
is  desirable  to  say  a  few  words  here  for  the  benefit  of  the  non- 
technical reader  who  desires  to  comprehend  thoroughly  what  the 
locomotive  engine  is. 

The  simple  steam  engine  consists  of  a  cast  iron  cylinder, 
bored  out  smooth  and  truly  circular  inside,  in  which  moves 
backward  and  forward  a  cast  iron  piston  in  the  edge  of  which 
are  turned  grooves.  In  these  are  placed  elastic  rings  of  steel 
or  brass,  which  press  outward  against  the  side  of  the  cylinder 
and  prevent  the  passage  of  steam.  The  steel  rod  which  is 
secured  to  the  piston  by  a  collar  and  nut,  goes  through  a  hole 
in  the  cover  at  one  end  of  the  cylinder.  It  passes  through  a 
stuffing  box,  which  is  filled  with  packing,  so  that  no  steam  can 
escape  round  the  rod  as  it  moves  backwards  and  forwards.  The 
outer  end  of  the  piston  rod  is  fitted  with  a  cross  head,  which 
travels  in  guides  to  compel  the  rod  to  move  in  a  straight  line. 
To  the  cross  head  is  jointed  one  end  of  the  connecting  rod,  the 
other  end  of  which  lays  hold  of  the  crank  pin,  and  as  the  piston 
moves  backwards  and  forwards  the  connecting  rod  alternately 
pulls  and  pushes  the  crank  pin  and  makes  it  rotate.  When  the 
piston  is  at  each  end  of  its  stroke  the  crank  is  on  a  "dead 
point,"  but  the  revolving  momentum  of  the  driving  wheel 
carries  the  crank  over  the  dead  point,  and  keeps  the  engine 
going,  and  besides,  there  are  always  at  least  two  engines  acting 
on  cranks  at  right  angles  to  each  other,  so  that  when  one  is  on 
the  dead  point  the  other  is  in  full  activity.  In  this  way,  the 
driving  wheels  are  made  to  revolve,  and  propel  the  locomotive. 
Steam  is  brought  to  bear  on  opposite  sides  of  the  piston  alter- 
nately in  the  following  way  : — In  the  cylinder  at  each  end  is 


200  THE  EAILWAY  LOCOMOTIVE 

made  a  port,  which  by  a  curved  passage  communicates  with  the 
valve  chest.  In  this  are  two  ports,  one  for  each  end  of  the 
cylinder,  and  between  them  a  third  port  which  communicates 
as  directly  as  possible  with  the  blast  pipe  already  described. 
The  ports  are  opened  and  closed  by  the  slide  valve,  which  is  in 
effect  a  shallow  box  with  very  thick  ends  and  sides.  The  cast 
iron  face  in  the  valve  chest  in  which  are  the  ports  is  made 
quite  flat  and  smooth,  and  on  it  rest  the  ends  and  sides, 
also  flat  and  smooth,  of  the  slide  valve.  The  valve  chest  is 
full  .of  steam  which  presses  the  valve  down  on  the  port  face 
or  seat.  The  exhaust  port  is  always  open  to  the  slide  valve 
inside.  As  that  moves  backwards  and  forwards  it  includes 

first  one  cylinder  port  and 
the  exhaust  port,  and  then 
the  other  cylinder  port  and 
the  exhaust  port.  When  this 
last  happens  the  steam  in  the 

Cylinder  "~~    cylinder  escapes  through  the 

pIG  67  box- slide  valve  and  exhaust 

port   up   the   chimney.      At 

the  same  time  the  slide  valve  opens  the  port  at  the  other  end 
of  the  cylinder,  so  that  steam  rushes  in  and  fills  the  cylinder, 
and  so  on  alternately  for  both  ends,  and  the  piston  is  moved 
backwards  and  forwards,  the  driving  wheel  revolves,  and  the 
exhaust  steam  escapes  up  the  chimney  and  causes  a  draught  in 
the  fire-box. 

The  accompanying  sketch,  Fig.  67,  will  make  what  has  just 
been  said  clear  at  a  glance.  A  is  the  slide  valve  in  section, 
B  the  bridle,  a  rectangular  frame  on  the  end  of  the  valve  spindle 
D  dropped  loosely  over  the  valve,  P  P  are  the  steam  ports,  and 
C  the  exhaust  port. 

The  first  locomotive  had  only  two  simple  cylinders.  In  the 
present  day  we  find  engines  with  two,  three,  and  four  cylinders 
arranged  in  different  ways.  However  by  far  the  larger  number 
of  locomotives  in  this  country  have  two  cylinders  only,  fixed 
between  the  frames.  In  the  United  States  always,  and  in  other 
countries  almost  always,  locomotives  have  outside  cylinders. 


CYLINDEES  AND  YALYES  201 

On  the  whole,  for  very  good  reasons,  the  inside  cylinder  is 
to  be  preferred.,  The  favour  shown  to  outside  cylinders  is 
due  partly  to  caprice,  in  part  to  certain  national  conditions. 
Thus  it  is  beyond  doubt  that  French  engineers,  and,  indeed, 
continental  engineers,  generally,  "  like  to  see  the  works."  They 
claim  that  all  the  parts  of  an  outside  cylinder  engine  are  more 
under  observation,  and  can  be  more  readily  cleaned  and  examined, 
and  kept  in  repair  than  those  of  an  inside  cylinder  locomotive. 
In  Europe  and  America  "  pits  "  are  unusual.  That  is  to  say, 
the  excavations  between  the  rails  over  which  a  locomotive  can 
stand  and  in  which  men  can  work  erect  on  the  machinery. 
Again,  a  cranked  axle  is  not  required,  and  greater  length  of 
bearings  can  be  had.  In  Europe  there  are  scarcely  any 
passenger  platforms,  and  engines  can  be  made  much  wider 
than  in  this  country,  which  means  that  there  is  plenty  of 
space  available  for  outside  cylinders.  Here  cylinders  up  to 
19  inches  in  diameter  have  been  used  outside,  but  the  arrange- 
ment is  more  cramped  than  it  is  abroad.  It  is,  of  course, 
true  that  the  platforms  are  not  necessarily  on  a  level  with 
the  cylinders.  But  it  would  not  do  to  let  the  cylinders  over- 
hang the  platform. 

In  the  United  States,  the  outside  cylinder  is  peculiarly  suited 
to  the  bar  frame.  In  the  same  way  the  inside  cylinder  goes 
naturally  with  the  plate  frame.  We  shall  deal  with  the  inside 
cylinder  engine  first. 

We  have  two  flat  frame  plates,  spaced  about  4  feet  1  inch  apart, 
between  these  must  be  fixed  the  cylinders.  If  these  are  18  inches 
in  diameter  they  will  occupy,  allowing  4  inches  for  the  cylinder 
walls,  3  feet  4  inches,  but  ports  cannot  be  worked  in  a  thick- 
ness of  1  inch.  Allowing  3  inches  for  each  cylinder  inside  we 
have  3  feet  8  inches,  which  leaves  only  5  inches  for  two  slide 
valves,  if  they  are  placed  vertically  between  the  cylinders.  This 
is  cutting  things  so  fine  that,  although  18  inch  cylinders  with 
the  valve  chest  between  them  have  been  used,  it  may  be  taken 
that  17  inches  is  the  largest  diameter  which  can  be  adopted. 
When  greater  dimensions  are  necessary,  the  valve  chests  are 
placed  on  the  tops  of  the  cylinders,  or  right  underneath  them. 


202 


THE  RAILWAY  LOCOMOTIVE 


On  the  Western  Eailway  of  France  locomotives  were  at  one 
time  running  with  the  cylinders  inside.  The  valve  chests  were 
outside  and  came  through  rectangular  apertures  cut  in  the 
plate  frames.  The  whole  of  the  valve  gear  was  outside, 
although  a  crank  shaft  of  the  normal  kind  was  used.  In  the 
United  States  slide-valve  chests  are  invariably  on  top  of  the 
cylinders,  the  slide  valves  being  actuated  by  rocking  shafts.  In 
this  country  top  valve  chests  are  usually  so  inclined  that  the 
valve  spindles  point  directly  to  the  centre  of  the  diameter  of  the 
crank  shaft. 

Formerly,  the  cylinders  were  always  cast  separately,  each 
with  its  valve  chest,  and  each  was  made 
with  a  heavy  flange  on  the  outside  to 
take  the  side  frame,  and  on  the  inside 
to  match  the  other  cylinder.  These 
flanges  were  all  planed  and  faced  up 
dead  true.  The  two  inside  flanges  were 
placed  in  apposition,  and  secured  to 
each  other  by  a  number  of  1J  inch 
bolts  turned  truly  cylindrical,  and  so 
tight  a  fit  in  carefully  drilled  holes  in 
the  flanges  that  they  had  to  be  driven 
home  with  a  heavy  hammer.  The  two 
cylinders  thus  became  ostensibly  one.  In  the  same  way  the  two 
outside  flanges  were  bolted  one  to  each  side  frame.  Excellent 
as  this  arrangement  is,  however,  it  was  found  that  in  practice 
the  cylinders  tended  to  work  loose  from  each  other,  and  from 
the  side  frames,  and  in  the  present  day  the  cylinders  are  almost 
always  cast  together  in  one  piece.  The  foundry  work  is  a  little 
more  expensive  and  there  is  more  risk  of  making  "  wasters,"  but 
the  result  is  much  more  satisfactory. 

Cylinders  are  always  cast  of  a  special  mixture  the  precise 
nature  of  which  is  usually  kept  as  a  secret  in  every  foundry. 
The  object  is  to  get  a  tough  cast  iron  which  will  not  crack,  and 
yet  will  be  just  as  hard  as  will  only  permit  it  to  be  bored  with 
some  difficulty.  Cylinders  wear  oval,  but  curiously  enough,  not 
on  the  bottom,  as  might  be  imagined,  because  it  has  to  carry 


FIG.  68. 


CYLINDEES  AND  YALYES  203 

the  weight  of  the  piston,  but  at  an  angle  such  as  shown  by  the 
dotted  line  in  the  accompanying  sketch,  Fig.  68. 

While  the  front  ends  of  the  cylinders  are  open  for  their  full 
diameter  in  order  that  the  pistons  may  be  put  in,  the  back  ends 
are  made  with  openings  of  not  more  than  half  the  diameter, 
which  are  closed  by  permanent  lids,  which  are  cast  in  one 
with  the  stuffing  boxes.  The  opening  at  the  back  end  is 
provided  because  it  facilitates  moulding  in  the  foundry,  and 
through  the  opening  is  passed  the  bar  which  in  the  boring 
machine  carries  the  cutter  head,  in  the  edge  of  which  are  the 
steel  boring  tools.  The  modern  boring  machine  is  invariably 
double.  It  has  two  horizontal  boring  bars  accurately  parallel, 
and  both  cylinders  are  bored  at  the  same  time.  The  boring 
bars  rotate  at  such  a  velocity  that  the  speed  of  the  boring  tool 
is  about  20  to  30  feet  per  minute,  depending  on  the  hardness  of 
the  cylinder.  The  harder  it  is  the  slower  the  cut.  Two  cuts 
usually  suffice,  one  a  roughing  cut  and  the  other  a  smoothing  cut. 
The  front  cylinder  cover  is  usually  cast  convex,  and  with  ribs  to 
give  it  strength.  It  may  have  to  support  a  load  of  20  to  30  tons. 
Its  flanges  are  carefully  faced  and  scraped  up,  as  are  the  flanges 
of  the  cylinder,  and  a  steam-tight  joint  is  secured  by  screwing 
up  the  nuts,  which  work  on  studs  screwed  into  the  cylinder 
flange,  sometimes  a  little  very  thin  red  lead  and  oil  are  smeared 
on  the  metal  faces,  and  when  the  cylinders  are  old  and  the  lids 
have  been  taken  off  and  put  on  several  times,  it  may  be 
necessary  to  interpose  a  ring  of  thin  brown  paper  which  has 
been  soaked  in  boiled  linseed  oil,  in  order  to  make  the  joint 
tight.  To  reduce  clearance  the  piston  is  cupped  to  fit  the 
convexity  of  the  cylinder  cover. 

Formerly  the  stuffing  box  in  the  back  cover  was  packed  with 
hemp  soaked  in  tallow.  In  the  present  day,  it  is  almost  always 
packed  with  white  metal  rings.  White  metal  is  an  alloy  of  tin, 
lead  and  antimony.  A  great  number  of  patents  have  been  taken 
out  for  metallic  packing.  This  packing  consists  of  a  number  of 
coned  segments  which  are  put  into  the  stuffing  box  and  surround 
the  rod.  As  the  "  gland "  is  screwed  down  it  will  be  seen  that 
the  cones  act  to  force  the  packings  against  the  rod  on  the  one 


204 


THE  RAILWAY  LOCOMOTIVE 


hand  and  the  sides  of  the  staffing  box  on  the  other.  In  some 
cases,  a  coiled  spring  is  used  to  press  the  segments  together. 
When  the  lubrication  is  attended  to  properly,  packing  of  this 
kind  gives  no  trouble  and  remains  quite  tight  for  several 
months. 

As  the  connecting  rod  works  at  various  angles  throughout 
each  revolution,  the  piston  rod  must  be  guided.  The  accom- 
panying sketch,  Fig.  69,  explains  why.  When  the  crank  A  is 
vertically  up  the  connecting  rod  is  pulling,  as  shown  by  the 
arrow.  If  the  length  of  the  rod  be  taken  as  the  pull  then  that 
pull  is  represented  by  two  forces ;  the  one  measured  by  the 
length  of  the  crank  tending  to  pull  the  crank  down  in  the 
direction  of  the  arrow,  the  other  precisely  equal  in  amount 


FIG.  69. 

at  the  other  end  of  the  connecting  rod  tending  to  lift  the 
cross  head  and  piston  rod  up.  If  the  pull  on  the  cross  head  was 
25,000  Ibs.,  and  the  connecting  rod  five  cranks  long,  then  the 
pull  tending  to  rotate  the  crank  would  be  20,000  Ibs.,  and  to 
push  the  crank  down  5,000  Ibs.,  and  to  lift  the  cross  head  up 
5,000  Ibs.  In  the  same  way,  when  the  crank  was  vertically 
downwards  the  connecting  rod  would  now  push  as  denoted  by 
the  arrow,  and  tend  still  to  force  the  crank  down  and  the  cross 
head  up  with  a  force  of  5,000  Ibs.  It  will  be  seen  that  the 
guides  must  withstand  very  heavy  vertical  stresses. 

There  are  three  systems  of  guiding  cross  heads  in  use. 
According  to  the  first  form,  rectangular  steel  bars  are  placed 
in  pairs,  one  pair  at  each  side  of  the  piston  rod.  Two  long  cast 
iron  blocks  slide  between  these  bars.  A  pin  passes  through 
both  blocks  and  the  cross  head  between  them,  and  on  the  pin 


CYLINDERS  AND   VALVES 


205 


206  THE  EAILWAY  LOCOMOTIVE 

works  the  small  end  of  the  connecting  rod.  The  arrangement  is 
illustrated  in  Fig.  70,  which  shows  a  very  excellent  engine  with 
Joy's  valve  gear,  designed  several  years  ago  for  the  Great  Eastern 
Kailway  by  Mr.  James  Worsdell.  AA  are  the  guide  bars. 
Across  the  engine,  about  3  feet  further  back  than  the  ends  of 
the  cylinders,  a  "motion  plate"  BB  is  bolted  between  the 
frames.  This  is  always,  in  the  present  day,  a  steel  casting 
shaped  to  be  as  strong  and  yefc  as  light  as  possible.  In  the 
casting  are  four  openings,  through  two  of  which  the  connecting 
rods  pass,  through  two  the  valve-gear  rods. 

On  the  face  of  the  motion  plate  are  provided  four  "snugs," 
through  each  of  which  is  a  hole.  The  stuffing  box  is  also 
provided  with  snugs  DD,  and  to  these  the  slide  bars  are  secured 
by  a  bolt  and  nut  at  each  end.  Between  the  bars  and  the  snugs 
are  placed  copper  plates.  When  the  engine  is  being  erected 
these  plates  can  be  reduced  in  thickness  by  filing,  so  that  the 
distance  between  the  slide  bars  can  be  regulated  with  the  most 
minute  accuracy.  This  form  of  guide,  with  certain  improvements 
and  modifications,  is  still  very  popular  for  inside  cylinder  engines 
with  which  alone  we  are  now  dealing. 

The  second  arrangement  is  simply  a  variant  of  that  just 
described  ;  only  two  guide  bars  are  used.  These,  instead  of  being 
at  the  sides,  so  to  speak,  of  the  piston  rod  are  fixed  one  over,  the 
other  under  it,  sufficiently  far  apart  to  clear  the  connecting  rod 
as  it  rises  and  falls.  The  cross  head  is  grooved  on  the  edges  to 
fit  the  slide  bars.  At  one  time  this  arrangement  was  very  much 
used  for  outside  cylinder  engines,  to  which  it  is  well  adapted. 

The  third  and  last  system  is  a  modification  of  a  marine  engine 
guide,  the  "  slipper  "  guide.  It  has  long  been  a  favourite  with 
Mr.  Drummond,  of  the  London  and  South  Western  Kailway,  and 
Mr.  James  Holden,  Chief  Mechanical  Engineer  of  the  Great 
Eastern  Railway,  used  it  almost  to  the  exclusion  of  all  other  systems. 
Fig.  71  is  a  longitudinal  section  of  a  cylinder  with  the  piston, 
cross  head  and  connecting  rod  as  fitted  on  the  Great  Eastern 
Railway ;  it  will  be  seen  that  only  a  single  heavy  bar  guide  is 
employed.  This  is  fixed  above  the  piston  rod,  and  on  it  slides 
the  "  slipper,"  really  a  species  of  box ;  B  is  the  motion  plate. 


CYLINDERS  AND  VALVES 


207 


208  THE  EAILWAY  LOCOMOTIVE 

When  the  engine  runs  chimney  first  the  thrust  due  to  the 
obliquity  of  the  connecting  rod  is  always,  as  we  have  seen, 
upwards  and  is  taken  by  the  solid  part  of  the  slipper.  When 
the  engine  runs  backwards  the  flat  plate  bolted  on  the  top  takes 
the  stress.  The  whole  arrangement  is  cheap,  easily  fitted  up 
with  great  accuracy,  and  easily  lubricated.  The  rubbing 
surfaces  are  very  large,  and  the  results  had  with  it  are  so 
satisfactory  that  all  the  engines  on  the  Great  Eastern  Kailway 
are  made  with  it.  In  the  larger  engines  the  piston  rod  is  pro- 
longed as  shown  and  passed  through  a  stuffing  box  in  the 
leading  cylinder  cover.  This  takes  some  of  the  weight  off  the 
bottom  of  the  cylinder.  It  may  be  added  here  that  when  super- 
heated steam  is  used  the  rod  must  be  carried  through  the 
front  cover  and  provided  with  a  guide  to  prevent  the  piston 
cutting  the  cylinder. 

The  small  end  of  the  connecting  rod  lays  hold  of  the  cross 
head  pin,  which  is  of  steel  hardened  on  the  outside.  Many  years 
ago  the  late  Mr.  Francis  Webb,  of  the  London  and  North  Western 
Eailway,  seeing  that  the  amount  of  movement  round  the  pin 
made  by  the  bearing  on  the  connecting  rod  is  quite  small,  did 
away  with  all  power  of  adjustment,  and  forced  into  the  end  of 
the  connecting  rod  a  solid  bush,  which  fits  the  pin  accurately. 
This  bush  is  shown  at  A  in  Fig.  71.  The  wear  is  extremely 
small.  When  the  bush  has  become  too  slack  on  the  pin,  wearing 
oval  and  beginning  to  knock,  it  is  forced  out  of  the  rod  by 
hydraulic  pressure  and  replaced  by  a  new  bush.  Previously, 
connecting  rods  were  fitted  at  both  ends  alike  with  brasses  which 
could  be  closed  up  on  the  pin  by  a  tapered  wedge,  known  as  a 
cotter,  D,  Fig.  70.  This  was  far  more  expensive  and  liable  to 
get  out  of  order  than  the  bush,  but  it  is  still  in  use  on  some  lines. 
As  for  the  "  big  end  "  of  the  connecting  rod — that  which  grasps 
the  crank  pin — there  are  many  patterns  in  use,  but  the  principle 
is  always  the  same.  We  have  either  the  strap  with  a  wedge 
cotter,  or  what  is  known  as  the  marine  big  end,  so  called  as  it 
is  almost  invariably  used  in  marine  engines.  Here  the  two 
brasses  of  the  connecting  rod  are  held  together  by  a  cap  and  two 
bolts  with  nuts. 


CHAPTER  XXVII 

FRICTION 

BEFORE  proceeding  further  it  is  desirable  to  call  attention  to 
the  question  of  friction.  It  is  a  very  interesting  fact  that  some 
of  the  loads  carried  by  journals  and  brasses  in  locomotive  engines 
are  far  heavier  than  can  be  regarded  as  safe  in  other  machinery. 
That  heating  occurs  so  rarely  is  due  to  accurate  workmanship,  the 
use  of  white  metal,  efficient  lubrication,  and,  above  all,  to  the 
rush  of  the  engine  through  the  air,  which  carries  off  the  heat. 
The  bearings  are  in  one  sense  too  small  for  their  loads,  because 
the  gauge — 4  feet  8J  inches  between  the  inner  faces  of  the  rails — is 
too  narrow  for  the  large  engines  now  in  use,  although  it  answered 
very  well  on  the  Stockton  and  Darlington  and  Wylam  colliery 
lines  on  which  the  first  "  Puffing  Billy  "  ran.  The  diameter  of  a 
crank  shaft  and  of  the  various  journals  on  it  may  be  increased, 
but  its  length  is  fixed  by  the  distance  between  the  inside  faces  of 
the  main  frame,  which  is  precisely  4  ft.  1  in.  The  accompanying 
table  gives  the  dimensions  of  a  crank  shaft  suitable  for  an  engine 
with  17  inch  cylinders,  24  inch  stroke,  four  coupled  wheels  6  feet 
7  inches  in  diameter,  and  160  Ibs.  boiler  pressure  : — 

CRANK  AXLE. 

Ft.  ins. 

Diameter  at  wheel  seat             0  9 

do.     at  bearings    ...         ...         ...         ...  0  7J 

do.     at  centre        ...          ...          ...          ...  0  7 

Distance  between  centre  of  bearings  ...         ...  3  10 

Length  of  bearing         ...          ...          ...          ...  0  9 

Diameter  of  crank  pin  ...          . , .          ...          ...  0  7  J 

Length  of  crank  pin     , , ,         ...         ...         ...  0  4  J 


210  THE  KAIL  WAY  LOCOMOTIYE 

As  has  been  said,  with  larger  engines  the  diameters  will  be 
greater,  and  with  smaller  less.  The  figures  given  are,  however, 
sufficient  for  our  present  purpose.  The  actual  effective  bearing 
surface  of  a  railway  axle  journal  may  be  taken  at  *3  of  its  total 
surface.  Now,  the  total  surface  of  a  bearing  7 J  inches  X  9  inches 
is  212*4  inches,  and  three-tenths  of  this  is  in  round  numbers 
64  inches.  The  load  on  each  main  bearing  may  be  taken  as 

7  tons,  or  15,680  Ibs.  and  — ^j—  =  245  Ibs.  per  square  inch, 

which  is  quite  a  moderate  load. 

The  conditions,  however,  as  regards  the  crank  pins  are  quite 
different.  Taking  the  average  cylinder  pressure  as  only,  75  Ibs. 
we  have  for  a  17  inch  cylinder  a  pull  and  push  on  the  crank 
pins  of  about  17,000  Ibs.,  and  32*4  as  the  available  bearing  area 

17  000 
in  square  inches.     Now,  -5^71  ~  —  521  Ibs.  as  the  load,  which 

o^'4 

is  very  heavy.  When  the  engine  is  starting  from  a  station  or 
climbing  a  bank  it  may  very  easily  reach  twice  this  with  a  boiler 
pressure  of  160  Ibs. 

It  may  be  said,  Why  not  make  the  crank  pins  longer  ?  The 
position  of  the  centre  of  the  length  of  the  crank  pins  is  fixed  by 
the  distance  between  the  centres  of  the  cylinders,  therefore  the 
crank  pins  must  be  lengthened  symmetrically,  if  at  all.  This  means 
that  either  the  main  bearings  must  be  shortened,  or  the  crank 
webs  reduced  in  thickness.  Now,  crank  axles  almost  always  break 
through  the  webs  when  they  break  at  all,  and  for  this  reason 
when  webs  are  rectangular  or  oval  in  shape  they  are  always  fitted 
with  wrought  iron  or  steel  safety  hoops  shrunk  on.  Various 
expedients  have,  however,  been  tried  to  get  over  the  difficulty. 
Mr.  James  Worsdell,  when  Locomotive  Superintendent  of  the 
North  Eastern  Kailway,  made  the  crank  webs  circular  discs.  In 
this  way  we  get  plenty  of  metal  at  the  weakest  part  of  the  web, 
and  are  enabled  to  thin  it  down,  and  so  lengthen  the  crank 
pins.  Abroad,  a  curious  arrangement  known  as  the  half-crank 
has  been  used.  The  driving  wheels  are  inside,  not  outside  the 
frames,  and  the  crank  shaft  does  not  pass  through  the  wheel. 
The  outer  end  of  the  crank  pin  is  secured  in  the  boss  of  the  wheel, 


FRICTION  211 

and  in  this  way  some  additional  length  is  obtained,  but  it  does 
not  appear  that  the  game  is  worth  the  candle. 

The  crank  shaft  of  a  locomotive  is  very  expensive.  It  is  forged 
out  of  solid  steel,  a  roughly  round  bar  with  two  lumps  of  metal 
on  it.  These  lumps  have  gaps  cut  in  them,  either  by  slotting 
out  the  metal  with  a  thin  tool,  or  by  a  cold  band  saw.  The 
crank  pins  and  bearings  are  all  subsequently  finished  in  the 
lathe.  In  marine  engines,  for  many  years,  the  built-up  crank 
shaft  has  been  used  with  great  success.  The  crank  webs  are 
separate  pieces,  as  well  as  the  crank  pins  and  the  plain  portion 
of  the  axle  ;  all  the  holes  are  drilled  and  the  parts  turned  with 
minute  accuracy,  and  the  whole  axle  is  then  put  together  under 
hydraulic  pressure.  The  result  is  a  cheap  crank  shaft,  thoroughly 
sound  and  good.  Mr.  D.  Drummond  has  used  this  type  of  crank 
axle  for  some  years  on  the  London  and  South  Western  Eailway. 
Built-up  cranks  are  also  coming  into  favour  in  America. 

Pistons  are  usually  made  of  tough  cast  iron,  although  steel  is 
not  infrequently  employed,  and  in  certain  cases  the  piston  and  its 
rod  are  forged  in  one  piece.  The  securing  of  a  piston  to  the  rod 
presents  some  difficulties  ;  practice  in  the  matter  varies.  As  a 
rule  a  tapered  hole  is  bored  in  a  boss  in  the  centre  of  the  piston. 
The  piston  rod  is  coned  at  the  end  to  fit  the  hole,  into  which  it 
is  drawn  very  tightly  by  a  nut  placed  on  the  screwed  end  of  the 
piston  rod  beyond  the  taper.  Some  designers  turn  a  collar  on 
the  rod,  as  at  E,  Figs.  70  and  71,  against  which  the  piston  is 
forced.  Others  only  use  a  set-off  at  the  base  of  the  cone.  If  the 
cone  is  too  tapered  the  piston  may  be  split.  The  nut  is  always 
liable  to  work  back  ;  many  engineers  maintain  that  the  only  way 
to  secure  it  with  certainty  consists  in  riveting  over  the  end  of 
the  rod.  Lock  nuts  and  cotter  pins  have  been  tried,  but  not,  it 
would  seem,  with  all  the  success  desirable.  On  some  lines  the 
tapered  portion  of  the  rod  is  screwed  into  the  piston.  The  piston 
packing  is  always  very  simple.  Many  years  ago  Mr.  Eamsbottom 
introduced  on  the  London  and  North  Western  Kail  way  three 
plain  steel  rings,  each  cut  through  in  one  place.  These  rings 
are  about  f  inch  square,  and  are  slipped  each  into  one  of  three 
similar  grooves  turned  in  the  circumference  of  the  piston, 

p  2 


212  THE  EAILWAY  LOCOMOTIVE 

and  their  own  elasticity  is  sufficient  to  keep  them  pressed  steam- 
tight  against  the  cylinder  walls.  Kamsbottom  rings  are  still 
very  and  deservedly  popular.  They  had  not  been  long  before 
the  world  before  a  precisely  similar  arrangement — in  all  respects 
but  one — known  as  Swedish  packing,  was  introduced.  The 
difference  lay  entirely  in  the  breadth  of  the  rings.  Two,  from 
f  inch  to  1  inch  wide  and  about  f  inch  thick,  are  used,  as  shown 
in  Fig.  71.  This  packing,  or  some  slight  modification  of  it,  is  to 
be  found  to-day  on  nearly  every  railway  in  the  world.  When 
the  steam  is  superheated  very  special  arrangements  are  required. 
It  may  be  added,  perhaps,  that  many  other  packings  have  been 
invented,  patented  and  tried.  But  the  advantage,  if  any,  which 
they  have  is  too  small  to  get  them  into  use. 


CHAPTEE   XXVIII 

VALVE    GEAR 

THE  action  of  a  slide  valve,  and  the  way  in  which  steam 
is  admitted  to,  and  discharged  from,  a  cylinder  has  already 
been  explained  in  a  rudimentary  way.  In  practice  the  valve 
gear  of  the  locomotive  has  been  made  the  subject  of  much 
invention,  and  of  papers  and  disquisitions  in  every  European 
language,  which  would  fill  volumes.  Simple  as  the  operation 
seems  to  be,  yet  so  much  depends  on  its  satisfactory  performance 
that  it  has  always  proved  an  attractive  subject  for  consideration. 
The  problems  presented,  thermodynamical  and  mechanical, 
lend  themselves  freely,  and  indeed  temptingly,  to  a  mathematical 
treatment  which  would  be  out  of  place  in  this  volume.  But 
much  can  be  said  quite  apart  from  mathematics  to  make  it  clear 
not  only  what  the  valve  gear  of  a  modern  locomotive  is,  but  why 
it  is  what  it  is. 

We  have  seen  that  the  normal  slide  is  moved  backwards  and 
forwards  on  its  seat,  placing  each  side  of  the  piston  alternately  in 
communication  with  the  steam  chest  in  which  the  slide  valve 
works,  or  with  the  exhaust  nozzle. 

Among  the  numerous  inventions  which  have  been  intended 
to  cause  the  movement  of  the  slide  valve,  only  three  are  in 
regular  extensive  use.  These  are  known  as  Stephenson's 
link  motion,  Joy's  radial  gear,  and  Walschaert's  gear.  The 
first  two  are  extensively  used  in  this  country.  On  the  Con- 
tinent, Walschaert's  gear  is  the  favourite ;  in  the  United  States, 
Stephenson's. 

In  the  first  locomotives  working  the  Liverpool  and  Manchester 
Eailway,  that  is  to  say,  the  real  progenitors  of  the  modern  rail- 
way engine,  motion  was  imparted  to  each  slide  valve  by  two 


214 


THE  RAILWAY  LOCOMOTIVE 


excentrics.  An  excentric  is  neither  more  nor  less  than  a  crank 
with  a  crank  pin  of  great  diameter.  The  "  throw  "  of  an  excen- 
tric, that  is,  its  virtual  crank  length,  is  measured  from  the  true 
centre  of  the  excentric  disc  to  the  true  centre  of  the  crank  axle. 
As  the  excentrics  could  not  be  put  on  the  crank  axle  because 
of  the  cranks,  if  they  were  each  made  in  one  piece,  they  are 
made  in  two  parts,  secured  together  by  sunken  bolts.  Each 
excentric  rod  had  at  the  end  what  was  known  as  a  "  gab  "  or 
notch,  which  dropped  on  a  pin  at  the  end  of  the  valve  spindle. 
One  of  the  excentrics  was  set  for  going  ahead,  the  other  forgoing 
backwards,  and  levers  were  so  arranged  that  the  driver  on  the 
footplate  could  lift  the  go-ahead  gabs  off  the  valve-spindle  pins 
and  drop  the  go-astern  gabs  on  when  he  wished  to  reverse  his 

engine,  and  vice  versa. 
But  it  was  quite  cer- 
tain that,  when  the 
go-ahead  gabs  were 
lifted  off,  the  valves 
would  be  in  such  a 
position  that  the  go- 
astern  gabs  would  not 
drop  on.  A  very 
simple  expedient  got  over  the  difficulty.  The  gabs  were  made  with 
long  horns  as  shown  in  Fig.  72  at  B  G.  The  distance  between  the 
horns  being  greater  than  the  travel  of  the  slide  valve,  it  mattered 
nothing  at  all  what  position  the  slide  valve  might  be  in.  It  was 
only  necessary  to  push  down  the  excentric  rod  hard,  and  the  horn 
would  slide  along  the  spindle  pin,  and  move  the  valve  until  the 
gab  dropped  on  to  it.  At  the  first,  two  reversing  levers  were  used, 
one  for  moving  the  go-ahead,  and  the  other  the  go-astern  excentric 
rods.  Then  a  bell  crank  was  added,  and  a  single  reversing  lever  F 
raised  one  and  dropped  the  other  pair  of  gabs.  The  next 
important  invention  consisted  in  simplifying  the  whole  arrange- 
ment by  turning  the  go-astern  gab  upside  down,  and  coupling 
the  two  rods  I  J,  by  two  links  D  D  to  the  bell  crank  E,  which 
was  moved  by  a  single  reversing  lever  on  the  footplate  by  the 
rod  F.  In  the  sketch,  A  is  the  slide-valve  spindle,  B  and  G 


FIG.  72. 


VALVE   GEAR  215 

the  horned  gabs,  C  is  the  crank  axle,  H  H  the  centres  of  the 
excen tries.  A  single  movement  then  sufficed  to  lift  one  gab  out 
of  gear  and  to  lift  the  other  in. 

The  reader  will  see  that  so  long  as  the  gab  was  retained,  the 
travel  of  the  slide  valve  must  remain  constant.  There  was  no 
means  of  varying  the  quantity  of  steam  admitted  to  the  cylinders 
but  the  regulator.  What  this  involves  will  be  explained  presently. 
In  the  early  years  of  railway  history  little  thought  was  given 
outside  a  very  narrow  circle  to  the  expansive  use  of  steam  in 
locomotive  engines.  However,  even  in  its  improved  form,  the 
gab  gear  was  not  quite  satisfactory.  It  was  noisy.  It  wore 
out  rapidly.  If  there  was  any  steam  in  the  valve  chests  the 
resistance  was  so  great  that  the  horn  would  not  move  the  valve, 
and  when  the  engine  was  running  fast  it  was  not  pleasant  gear 
to  handle. 

Various  inventors  sought  improvements,  and  finally  arrived 
the  link  motion.  The  genesis  of  this  is  doubtful,  and  a  keen 
controversy  exists  as  to  the  way  in  which  it  came  into  being. 

So  far  as  can  be  ascertained,  a  pattern  maker  named  Howe 
showed  Eobert  Stephenson  a  model  of  an  invention  which,  to 
judge  from  the  drawings  existing,  would  not  work.  He  used 
extremely  short  excentric  rods,  and  coupled  their  ends  by  a 
slotted  bar  or  link.  Into  the  slot  was  put  a  pin  on  the  end  of 
the  valve  spindle,  and  by  moving  the  link  up  or  down,  either 
one  excentric  or  the  other  drove  the  valve.  But  the  rods  were  so 
short  that  the  excentrics  could  not  get  round.  Nevertheless,  here 
in  one  way  was  the  rudimentary  idea  of  the  link  motion.  In 
1898,  Mr.  W.  P.  Marshall  read  a  paper  before  the  Institution  of 
Civil  Engineers  on  "  The  Evolution  of  the  Locomotive  Engine." 
Speaking  of  valve  gear,  he  writes :  "  In  1841,  when  I  was  Locomotive 
Superintendent  of  the  North  Midland  Eailway,  I  was  making  trial 
of  different  valve  motions  for  Mr.  Robert  Stephenson,  and  on  the 
15th  December,  1841,  Mr.  Stephenson  came  into  the  locomotive 
office,  Derby,  on  the  way  back  from  Newcastle,  and  said,  '  There 
is  no  occasion  to  try  any  further  at  scheming  valve  motions,  one 
of  our  people  has  now  hit  on  a  plan  that  beats  all  the  other  valve 
motions,'  and  he  then  explained  the  slotted  link.  In  1842  an 


216 


THE  EA1LWAY  LOCOMOTIVE 


engine  with  the  link  motion  was  delivered  by  Messrs.  Stephenson 
&  Co.  to  the  Northern  Midland  Railway."  No  particulars  are 
available  of  this  engine,  but  the  probability  is  that  the  motion 
was  very  like  that  now  in  use. 

The  entire  episode  is  very  curious.     It  illustrates  the  way  in 

which  the  obvious  is  some- 
times missed.  If  the  reader 
will  examine  Fig.  72  he 
will  see  that  if  the  ends  of 
the  horns  were  joined  to- 
gether the  links  D  D  might 
be  dispensed  with.  Instead 
of  the  gabs  being  in  one 
piece  with  the  rods,  pin 
joints  would  be  needed  at  K  K.  If,  further,  the  horns  were  closed 
in  as  shown  by  the  dotted  lines,  the  link  was  at  once  obtained. 
To  curve  it  to  the  radius  of  the  excentric  rods  would  follow  as  a 
matter  of  course,  and  the  link  motion  as  shown  in  Fig.  73  would 
then  be  complete.  The  gear  is  always  identified  with  Stephenson, 
and  it  seems  probable  that  while  he  was,  so  to  speak,  put  on  the 
track  by  Howe,  he  really  followed  much  the  line  of  reasoning  just 
sketched  out,  and  so  produced  a  valve  gear  which  is  immortal 
among  mechanical  devices. 


FIG.  73. 


CHAPTEK   XXIX 

EXPANSION 

IT  is  desirable  here  to  interrupt  the  description  of  valve  gear, 
and  deal  with  general  principles,  because  until  these  are  mastered 
the  reason  why  valve  gears  are  not  all  alike  will  not  be  apparent. 

It  is  assumed  that  the  majority  of  readers  understand  the  great 
principles  of  thermodynamics  sufficiently  well  to  appreciate  the 
nature  of  the  advantages  gained  by  working  steam  expansively. 
Nevertheless,  in  pursuance  of  the  scheme  of  this  book,  it  is 
necessary  to  offer  here  a  few  words  of  explanation. 

Let  us  suppose  that  gab  gear  is  in  use,  and  that  the  cylinder 
is,  when  the  piston  reaches  the  end  of  its  stroke,  nearly  full  of 
steam.  It  will  not  be  of  much  less  pressure  than  that  in  the 
boiler.  Suppose  the  capacity  of  the  cylinder  is  two  cubic  feet, 
and  the  cylinder  pressure  at  the  moment  the  exhaust  opens  is 
75  Ibs.  per  square  inch,  then  two  cubic  feet  of  steam  of  that 
pressure  is  blown  into  the  atmosphere  to  waste ;  yet  it  is  quite 
obvious  that  there  is  plenty  of  work  still  in  this  steam.  Let  us 
suppose  now,  further,  that  the  supply  of  steam  to  the  cylinder  is 
stopped  when  the  piston  has  gone  half  way,  the  exhaust  remain- 
ing unchanged.  It  follows  that  at  the  end  of  the  stroke  we  shall 
have  one  cubic  foot  of  steam  at  75  Ibs.  pressure  supplied,  which 
becomes  two  cubic  feet  at  the  end  of  the  stroke.  Its  volume  is 
doubled  and  its  pressure  will  be  half  75  Ibs.,  or  37*5  Ibs.  Thus 
not  only  shall  we  use  only  half  the  total  quantity  of  steam  used 
before,  but  we  shall  send  that  half  up  the  chimney  with  only  one- 
half  as  much  available  work  in  it.  The  loss  so  far  will  be  reduced 
to  one-fourth  of  what  it  was. 

It  must,  however,  not  be  forgotten  that  the  work  done  in  the 
cylinder  at  each  stroke,  therefore,  at  each  revolution  of  the  driving 


218 


THE  RAILWAY  LOCOMOTIVE 


wheel  will  be  less  than  before  ;  but  not  so  much  less  as  to 
neutralise  the  economical  advantage  gained.  This  will  best  be 
made  clear  by  a  numerical  example.  Let  a  cylinder  be  17  inches 
in  diameter  ;  the  piston  surface  227  square  inches  ;  length  of 
stroke  24  inches  ;  capacity  of  cylinder  227  X  24  =  5,448  cubic 
inches  ;  pressure  of  steam  150  Ibs.,  working  without  expansion, 
steam  being  admitted  for  the  whole  stroke  ;  piston  speed  600  feet 

per  minute  ;   we  have  then  -  —   -  =  619  h.p. 


Next  let  us  suppose  that  steam  is  cut  off  at  half  stroke,  all 

the  other  conditions  remain- 
ing the  same.  The  quantity 
of  steam  used  per  stroke  will 
then  be  2,724  cubic  inches; 
the  average  pressure  will 
obviously  be  less  than  150 
Ibs.  It  will  be  150  Ibs.  up 
to  half  stroke,  and  it  will  be 
75  Ibs.  at  the  end  of  the 
stroke.  The  average  pres- 
sure is  found  by  the  following 
FIG.  74.  ruie  :_ 

Add  1  to  the  hyperbolic  logarithm  of  the  ratio  of  expansion. 
Multiply  the  result  by  the  initial  pressure,  and  divide  by  the  ratio 
of  expansion ;  the  quotient  is  the  average  pressure.  The  ratio 
of  expansion  is  2,  and  the  hyperbolic  logarithm  of  2  is  *6931. 

We  have,  therefore,  -      — » —      -  —  103*965  Ibs.  as  the  average 

pressure,  or,  in  round  numbers,  104  Ibs.,  and 
227  X  104  X  6 


3300 

that  is  to  say,  we  get  about  two-thirds  the  power  for  one-half 
the  steam. 

For  a  full  explanation  of  what  a  hyperbolic  logarithm  is, 
the  reader  is  referred  to  any  treatise  on  logarithms.  A  gas 
expanding  exerts  pressure  in  an  inverse  ratio  to  the  space  it 
occupies.  The  curve  of  falling  pressure  is  therefore  a  hyperbola. 


EXPANSION 


219 


The  accompanying  diagram,  Fig.  74,  will,  it  is  hoped,  make  the 
facts  clear.  Here  we  have  a  piston  P  moving  in  a  cylinder  A  B  C  D. 
The  first  portion  of  the  stroke  A  Gr  C  H  being  made  with  full 
pressure,  is  denoted  by  1  in  the  formula  given  above.  The  second 
half  of  the  stroke  being  done  expansively,  we  have  our  hyperbolic 
curve  of  falling  pressure,  shown  by  the  line  2.  The  logarithm 
denotes  the  proportion  which  the  space  E,  which  represents  work 
done  during  expansion,  bears  to  the  area  of  the  rectangle  A  G  C  H, 
which  represents  the  work  done  during  the  full  pressure  part  of 
the  stroke. 

In  the  following  table  are  given  a  few  of  the  hyperbolic  log- 
arithms most  likely  to  be  wanted  in  locomotive  practice : — 

HYPERBOLIC  LOGARITHMS. 


Ratio  of  Expansion. 

Hyperbolic  Logarithms. 

2-0 

0-6931 

2-5 

0-9163 

3-0 

1-0986 

3-5 

1-2528 

4-0 

1-3863 

4-5 

1-5041 

5-0 

1-6994 

5-5 

1-7047 

6-0 

1-7918 

6-5 

1-8718 

70 

1-9459 

It  must  be  understood  that  what  has  just  been  said  is  intended 
only  to  exemplify  a  principle.  The  expansive  working  of  steam 
is  really  not  simple,  but  complex.  The  ratio  of  expansion  is 
always  less  than  that  given  above,  because  the  piston  does  not 
touch  the  cylinder  cover ;  and  the  clearance  space,  as  it  is  called, 
is  filled  with  steam,  so  that  the  whole  quantity  expanding  is 
greater  than  is  represented  by  the  volume  swept  out  by  the 
piston  at  each  stroke.  Again,  steam  is  always  condensed  when 
it  first  enters  the  cylinder,  unless  it  has  been  superheated ;  and 
the  expansion  curve  is  never  a  true  hyperbola,  except  by  accident. 
The  reader  possessed  of  a  fair  knowledge  of  Thermodynamics 


220  THE  RAILWAY  LOCOMOTIVE 

does  not  need  detailed  explanations  of  what  takes  place  inside  a 
cylinder.  The  reader  who  does  not,  has  had  so  much  explained 
as  will  enable  him  to  comprehend  what  follows  about  the  action 
of  the  Stephenson  link,  and  nothing  more  is  necessary  here. 

Let  it  be  supposed  that  the  slide  valve  is  made  of  such  a  length 
that  when  in  the  middle  of  its  stroke  it  just  covers  all  the  ports. 
Then  it  follows  that  if  it  is  moved  either  forward  or  backward  it 
will  admit  steam  to  the  front  or  back  end  of  the  cylinder.  Under 
such  conditions  there  could  be  no  expansive  working.  The 
steam  must  follow  the  piston  full  stroke,  because  the  moment 
steam  was  cut  off  at  one  end  of  the  cylinder  it  would  be  admitted 
at  the  other. 

But  let  the  valve  be  lengthened,  so  that  it  will  more  than  cover 
the  ports.  Under  these  conditions,  as  shown  in  the  diagram 
Fig.  67,  and  the  sectional  drawing  Fig.  79,  both  the  valve  and 
the  piston  would  have  to  move  some  distance  before  the  port 
opened  for  the  admission  of  steam.  But  the  valve  would  also 
cut  steam  off  before  the  stroke  of  the  piston  was  complete.  Here 
then  we  have  expansion.  If  now  the  excentric,  instead  of  being 
set  at  an  angle  of  90°  with  the  crank,  is  moved  forward,  then  we 
shall  have  steam  admitted  at  the  beginning  of  the  stroke,  and  cut 
off  before  the  end.  The  extra  length  of  valve  is  called  the  "  lap"  ; 
the  angular  advance  of  the  excentric  is  called  the  "lead,"  and 
the  lap  and  lead,  it  will  be  readily  understood,  are  two  very 
important  factors  in  the  working  of  the  valves  of  a  locomotive 
engine.  The  lead  virtually  cancels  the  lap  so  far  as  admission 
is  concerned,  and  augments  it  by  an  equal  amount  so  far  as  cut- 
off is  concerned. 

In  Great  Britain  long  practice  has  fixed  1  inch  as  the  amount 
of  lap  which  best  meets  all  the  working  conditions.  In  a  few 
cases  it  is  only  -J  inch,  while  in  others  1J  inch  has  been  tried. 
But  999  out  of  every  1,000  locomotives  fitted  with  slide  valves 
have  a  lap  of  1  inch. 

Now  if  a  slide  valve  has  a  lap  of  1  inch,  when  it  is  at  rest  in 
mid  stroke  it  overhangs  the  port  at  each  end  by  1  inch,  and  it 
must  be  moved  at  least  1  inch  in  either  direction  before  it  will 
open  a  port.  It  will  be  seen,  therefore,  that  the  valve  spindle 


EXPANSION  221 

pin  must  be  some  way  from  the  centre  of  the  link  in  either  direc- 
tion before  the  engine  can  take  steam.  Furthermore,  let  it  be  sup- 
posed that  the  arrangement  of  the  valve  gear  is  such  that  steam 
is  cut  off  in  one  cylinder  at  something  less  than  three-quarter  stroke. 
It  will  then  be  admitted  to  the  other  cylinder  while  the  crank  is 
near  the  dead  point.  Then,  with  a  moderately  heavy  train,  the 
engine  will  not  start.  In  railway  phraseology  "she  has  gone 
blind,"  that  is  to  say  a  port  is  blinded  or  stopped  by  the  lap  on 
the  slide  valve,  and  the  piston  which  would  pull  the  crank  round 
gets  no  steam  or  is  so  near  the  dead  point  that  it  cannot  start 
the  train.  To  get  the  engine  to  start,  it  must  be  reversed  in 
order  to  put  the  valves  into  a  new  position.  Every  railway 
traveller  has  seen  the  regulator  opened  and  no  result  follow. 
Then  he  has  seen  the  reversing  screw  turned,  and  the  whole 
train  pushed  back  a  yard  or  so.  Then  the  wheel  being  again 
turned  the  valves  are  put  in  full  forward  gear  and  the  train  goes 
on  its  way.  One  reason  for  keeping  lap  down  to  an  inch  is  that 
the  longer  the  lap  the  greater  is  the  risk  of  the  engine  going 
blind. 

Lap  and  lead  can  be  so  adjusted  to  each  other  that  when  the 
engine  is  in  full  gear  for  running  in  either  direction,  the  steam 
will  always  be  cut  off  at  a  fixed  point  of  the  stroke.  What  this 
fraction  may  be  varies.  Generally  speaking  it  may  be  taken  at 
about  75  per  cent.,  but  the  old  gab  gear  would  do  as  much.  The 
link  when  in  full  gear  is  only  the  gab  improved  mechanically  in 
constructive  detail. 

If  now,  leaving  everything  else  as  it  was,  we  shorten  the  throw 
of  the  valve,  it  will  be  seen  that  the  steam  port  at  each  end, 
although  not  opened  fully,  may  be  opened  sufficiently  to  admit 
steam ;  but  the  shorter  the  stroke  of  the  valve  the  less  time  will 
the  port  remain  open.  In  other  words,  the  shorter  the  stroke  of 
the  valve  the  earlier  in  the  stroke  of  the  piston  will  steam  be  cut 
off,  and  the  higher  will  be  the  ratio  of  expansion.  The  stroke 
can  be  shortened  by  moving  the  link  so  that  the  valve  spindle 
pin  is  not  at  the  end  of  the  link,  but  somewhere  nearer  the  middle 
of  its  length.  In  this  way  the  Stephenson  link  possesses  the 
great  merit  of  giving  the  driver  the  power  of  varying  the  amount 


222  THE  EAILWAY  LOCOMOTIYE 

of  expansion.  When  climbing  a  hill,  for  instance,  he  puts  the 
engine  in  full  forward  gear  to  get  the  maximum  pulling  effort. 
On  a  level  he  "  links  her  up,"  and  cutting  off  earlier  he  works 
expansively. 

It  is  most  important  that  the  student  should  master  com- 
pletely the  parts  played  by  lap  and  lead.  If  these  are  once 
understood  there  will  be  little  difficulty  in  following  out  the 
details  of  any  gear  however  complicated.  To  this  end  no 
mathematics  are  needed.  The  facts  may  be  readily  mastered  by 
cutting  a  valve  in  section  out  of  thin  cardboard,  and  moving  it 
backwards  and  forwards  on  a  section  of  the  port  face.  The 
diagram  Fig.  67  may  be  utilized  for  this  purpose. 


CHAPTER  XXX 

THE    STEPHENSON    LINK    MOTION 

UP  to  this  point,  the  link  has  been  spoken  of  as  moving  on  a 
fixed  centre  coincident  with  the  centre  of  its  own  length.  No 
such  condition,  however,  exists  in  a  locomotive  ;  on  the  contrary, 
the  real  movement  of  the  link  is  very  complicated.  The  geometry 
of  the  link  motion  has  been  made  the  subject  of  careful  study  by 
mathematicians.  The  reader  will  find  at  the  end  of  the  volume 


FIG.  75. 

a  list  of  authors  who  may  be  consulted  on  this  subject  with 
advantage.  Nothing  more  can  be  dealt  with  here  than  principles. 

It  will  be  seen  that  if  the  excentrics  were  placed  opposite  each 
other,  a  line  drawn  through  their  centres  also  passing  through 
the  centre  of  the  axle,  the  link  might  be  carried  on  a  fixed  pin  at 
the  centre  of  its  length,  on  which  it  would  rock  backwards  and 
forwards.  In  that  case  only  one  excentric  would  be  required  as 
in  Walschaert's  gear.  But  a  line  drawn  from  centre  to  centre  of 
the  excentrics  cannot  pass  through  the  centre  of  the  axle  because 
of  the  angular  advance  or  lead  of  each  excentric. 

The  sketch,  Fig.  75,  will  make  this  clear.  Here  A  is  the  crank 


224  THE  RAILWAY  LOCOMOTIVE 

axle,  B  is  the  crank  pin,  F  is  the  valve  spindle,  C  is  the  go-ahead 
excentric,  D  is  the  go-backwards  exceiitric,  E  is  the  centre  line  of 
the  slot  in  the  link.  If  now  there  were  to  be  no  angular  advance 
of  the  excentrics,  and  no  lead,  they  would  be  so  keyed  on  the 
axle  that  their  centres  H  H  would  fall  on  a  vertical  line  uniting 
G  G.  They  would  consequently  be  set  each  at  an  angle  of  90° 
with  the  crank,  and  the  link  could  rock,  as  stated  above,  on  the 
centre  M,  and  when  the  reversing  lever  was  in  mid  gear  the  slide 
valve  would  have  no  movement.  But  the  centres  of  the  excentrics 
not  being  opposite  to  each  other,  their  throws  do  not  neutralise 
each  other.  Let  the  dotted  lines  show  the  position  when  the 
crank  has  made  half  a  revolution.  It  will  be  seen  that  a  vertical 
line  joining  the  centre  of  the  excentrics  has  now  been  carried  as 
far  behind  the  centre  of  the  crank  axle  as  it  previously  was  in 
front  of  it,  and  the  whole  link,  and  with  it  the  valve  spindle 
F,  has  been  shifted  through  a  distance  equal  to  that  between 
N  and  M.  Consequently  there  is  no  position  in  which  the  slide 
valve  can  be  absolutely  at  rest  while  the  engine  is  running.  A 
curious  result,  by  no  means  generally  known,  is  that  if  a  loco- 
motive is  running  chimney  first  and  the  link  is  put  in  mid  gear, 
the  engine  will  continue  to  run  forward  because  the  valve  will 
give  a  little  steam  to  the  cylinder  at  each  end  of  the  stroke  by 
reason  of  the  movement  M  N.  If  the  engine  happens  to  be 
running  tender  first,  then  in  like  manner  it  will  continue  to  run 
backwards.  Of  course,  it  must  be  understood  that  the  loads  are 
light.  A  search  for  an  explanation  of  this  phenomenon  will 
constitute  an  interesting  exercise  for  the  student.1 

As  no  point  in  the  link  is  at  rest  when  the  engine  is  in  motion, 
and  the  link  as  a  whole  is  moved  backwards  and  forwards  as 
well  as  each  end,  the  link  must  be  itself  carried  by  a  link, 
which  may  be  pivoted  at  the  top,  at  the  bottom,  or  in  the  middle, 
no  matter  which,  so  far  as  the  movement  is  concerned.  This 
suspending  link,  playing  like  a  pendulum,  causes  the  centre  of 
the  main  link  to  rise  and  fall,  through  only  a  small  distance  it  is 
true,  yet  small  as  it  is  it  affects  the  travel  of  the  valve.  The 

1  The  author's  attention  was  first  called  to  this  fact  by  the  late  Sir  Frederick 
Bramwell. 


THE   STEPHENSON  LINK  MOTION  225 

usual  practice  is  to  suspend  the  link  by  the  middle,  occasionally 
at  the  lower  end,  never  by  the  top  in  the  present  day.  A  further 
complication  is  introduced  by  the  angular  movement  of  the 
connecting  rod.  The  piston  is  not  in  the  middle  of  its  stroke 
when  the  crank  is  vertically  up  or  down  by  an  amount  equal  to 
the  versed  side  of  the  arc  described  by  the  big  end  of  the  rod.  All 
difficulties  have,  however,  been  got  over,  and  a  well-designed 
Stephenson  gear  gives  a  completely  harmonious  action  of  the 
slide  valves,  and  is  in  every  way  but  two  quite  satisfactory.  The 
lead  is  not  constant  in  the  first  place,1  and  in  the  second,  when 
the  engine  is  working  expansively  and  running  fast,  the  admission 
port  is  never  opened  fully  and  is  kept  open  only  for  a  minute 
fraction  of  a  second.  The  result  is  that  steam  is  wiredrawn,  and 
it  is  impossible  to  get  a  good  pressure  in  the  cylinder,  and  for 
the  same  reason  the  exhaust  is  throttled,  and  the  exhaust  port 
closed  too  soon.  Various  means  of  getting  over  the  difficulty 
have  been  schemed,  but  as  none  of  them  are  in  use,  save  experi- 
mentally, no  more  need  be  said  of  them  here. 

The  details  of  construction  are  very  simple  and  so  familiar 
that  no  further  illustrations  are  necessary.  The  link  is  dropped 
down  for  running  chimney  first,  and  raised  up  for  running 
backwards.  A  weigh  bar  runs  across  under  the  barrel  of  the 
boiler,  and  is  carried  in  plain  bearings  bolted  to  the  main  frames. 
On  the  weigh  bar  are  keyed  four  arms.  Two  of  them,  extending 
forward,  carry  each  one  of  the  links  by  a  pair  of  sling  bars.  The 
third,  always  placed  halfway  between  the  frames,  extends  back- 
wards and  carries  a  cheese- shaped  block  of  cast  iron,  which 
exactly  balances  the  weight  of  the  links  and  half  that  of  the 
excentric  rods.  The  fourth  arm  usually  stands  up  at  the  side 
of  the  boiler,  and  to  it  is  joined  a  long  flat  bar  extending  to  the 
driver's  cab.  Here  in  the  older  locomotives  it  is  coupled  to  the 
reversing  lever,  which  moves  in  an  arched  guide,  provided  with 
notches  into  which  drops  a  detent,  which  can  be  lifted  out  by  a 
small  subsidiary  lever  just  in  front  of  the  handle.  When  the 
reversing  lever  is  drawn  back  the  link  motion  is  raised  by  the 

1  The  student  will  do  well  to  master  the  effect  of  "  crossed"  and  "  open  " 
excentric  rods  on  lead. 

B.L.  Q 


226 


THE   EAILWAY  LOCOMOTIVE 


weigh  bar  and  the  notch  in 
which  the  detent  is  placed 
determines  the  point  of 
cut-off  and,  as  explained, 
the  ratio  of  expansion.  Too 
much  precaution  cannot  be 
used  in  securing  the  balance 
weight,  which  is  very  liable 
to  work  loose  and  fall  off. 
A  terrible  accident  occurred 
some  years  ago  on  the 
Great  Eastern  Eailway. 
Two  trains  were  about  to 
pass  each  other  when  the 
balance  weight  of  one 
engine  fell  on  the  line  and, 
rolling  under  the  other 
train,  derailed  a  wheel  and 
threw  the  engine  off  the 
rails.  In  the  United  States 
the  balance  weight  is 
seldom  used.  It  is  re- 
placed by  a  powerful  coiled 
spring  round  the  weigh 
bar  shaft  or  a  flat  trans- 
verse spring  between  the 
frames.  The  reversing 
lever  has  been  superseded 
in  all  modern  locomotives 
by  a  hand-wheel  and  quick 
threaded  screw. 

In  many  modern  engines 
power  is  employed  with 
much  ingenuity  to  work 
the  valve  gear.  About  15 


years   ago  Mr.   Stroudley,  Locomotive   Superintendent   of   the 
London,  Brighton  &  South  Coast  Eailway,  used  the  air  pressure 


THE   STEPHENSON   LINK  MOTION 


227 


FIG.  77. — Wain wright's  reversing  gear. 

of  the  Westinghouse  brake  for  this  purpose.     More  recently  Mr. 
Drummond,  of  the  London  &  South  Western  Kailway,  fitted  steam 

Q2 


228 


THE  KAILWAY  LOCOMOTIVE 


reversing  gear  to  his  largest  engines.     Then  Mr.  H.  Wainwright, 
Chief  Mechanical  Engineer,  London,  Chatham  &  Dover  and  South 


Steel  Tube 


FIG.  78. — Wain  Wright's  reversing  gear. 

Eastern  Eailway,  designed,  and  has  for  a  long  time  used,  the 
arrangement  illustrated  by  Figs.  76,  77,  and  78.  At  the  right- 
hand  side  of  the  boiler  barrel  is  fixed  a  small  vertical  bed  plate 
carrying  a  steam  and  a  water  cylinder  shown  in  section  in  Fig.  77. 


THE  STEPHENSON  LINK  MOTION  229 

The  admission  of  steam  to  the  upper  cylinder  is  controlled  by 
the  small  slide  valve  shown  in. the  section  Fig.  77.  This  is 
worked  from  the  footplate  by  a  miniature  reversing  lever ;  a 
second  lever  controls  the  admission  of  steam  and  water. 

The  lower  cylinder  is  what  is  known  as  a  "  cataract " — a  term 
derived  from  old  Cornish  engine  practice — a  leather-packed  piston 
having  water  at  both  sides  of  it.  Water  being  incompressible, 
so  long  as  that  in  the  cataract  cylinder  is  locked  up  the  piston 
cannot  move.  The  upper  or  steam  cylinder  piston  being  on  the 
same  rod,  it  also  is  fixed.  It  follows,  therefore,  that  the  rod  being 
linked  as  shown  to  the  weigh  bar,  already  mentioned,  of  the 
Stephenson  valve  gear,  the  gear  is  efficiently  locked  in  position 
by  the  cataract.  If  the  driver  wishes  to  reverse  the  engine  he 
can  turn  on  steam  to  the  steam  cylinder  above  or  below  the 
piston,  as  he  wishes  to  go  backwards  or  forwards,  by  altering 
the  position  of  the  slide  valve,  to  the  steam  chest  of  which  he  has 
admitted  boiler  steam.  But  the  piston  cannot  rise  or  fall  until 
the  position  of  the  water-cock  is  changed  and  water  is  permitted 
to  pass  from  one  side  of  the  cataract  piston  to  the  other.  A  small 
indicator  moving  on  a  plate  in  the  cab  shows  the  precise  per- 
centage of  the  stroke  during  which  steam  is  admitted.  The 
details  are  so  clearly  given  that  further  description  does  not 
appear  to  be  required.  This  reversing  gear  acts  with  great 
steadiness.  No  labour  or  risks  are  incurred  by  the  driver  in 
handling  the  engine,  and  the  point  of  cut-off  can  be  settled  with 
much  greater  minuteness  than  is  possible  with  a  lever  and  a 
notched  quadrant. 


CHAPTER   XXXI 


THE  principles  involved  in  the  construction  of  Walschaert's 
gear  are  in  many  respects  identical  with  those  of  the  Stephenson 
link,  lap  and  lead  playing  the  same  part.  Let  us  suppose  that  it  is 
hung  on  a  fixed  pivot  in  the  middle  and  worked  by  a  single 
excentric  only.  The  excentric  rod  being  attached  to  the 
link  at  the  lower  end,  the  excentric  must  be  keyed  on  the  crank 
axle  precisely  at  right  angles  to  the  crank,  and  the  crank  will 
rock  backwards  and  forwards  on  its  centre  pin.  If  now  the 
pin  at  the  end  of  the  valve  spindle  were  placed  at  the  upper  end 
of  the  link,  the  engine  would  go  ahead.  To  reverse  it  we  have 
only  to  drop  the  pin  to  the  bottom  of  the  link.  The  length 
of  the  travel  of  the  valve  will  be  determined  by  the  place  of  the 
pin  in  the  link  just  as  it  is  with  the  Stephenson  link.  But 
such  an  arrangement  gives  no  lead.  This  might  be  got,  how- 
ever, by  giving  the  excentric  sufficient  angular  advance.  But  if 
this  were  right  for  going  ahead,  it  would  be  absolutely  wrong 
for  running  backwards,  and  therefore  quite  unfit  for  a  locomotive. 
In  practice,  as  the  gear  is  usually  fitted  to  outside  cylinders,  no 
excentric  is  used.  Instead,  a  small  counter  crank  is  carried  by 
the  main  crank  pin,  and  this,  precisely  at  right  angles  to  the 
main  crank  and  much  shorter,  is  coupled  by  a  plain  straight  bar 
to  the  reversing  link. 

Lead  is  obtained  in  the  following  way.  The  radius  rod,  that 
is  to  say,  a  rod  one  end  of  which  can  be  raised  or  lowered  in  the 
rocking  link,  is  not  coupled  directly  to  the  valve  spindle,  but  to 
a  swinging  or  "  floating  "  lever.  To  the  upper  end  of  this  the 
valve  spindle  is  jointed.  The  lower  end  of  it  is  coupled  to  the 
cross  head  by  an  arm  extending  downwards.  A  glance  at  the 


WALSCHAEBTS  AND  JOY'S   GEA&S  231 

engraving  on  p.  232  will  suffice  to  show  that  when  the  piston  has 
reached  the  end  of  the  cylinder,  the  slide  valve  will  have  been 
pushed  forward  by  the  floating  lever,  and  nothing  more  is 
required  to  get  the  precise  amount  of  lead  wanted  than  to 
proportion  properly  the  lengths  of  the  two  arms  of  the  swinging 
lever. 

Fig.  79  shows  this  gear  as  fitted  to  the  high  pressure  cylinder 
of  an  American  compound  engine  of  the  celebrated  De  Glehn 
type.  The  engine  has  a  balanced  slide,  the  pressure  being 
kept  off  the  top  of  it  by  a  ring  fitted  with  packing  to  the  inside 
of  a  second  ring,  the  upper  edge  of  which  moves  steamtight  on 
the  lid  of  the  valve  chest.  A  is  the  crank  axle,  B  is  the  counter 
crank,  forged  in  one  with  the  crank  pin.  D  is  the  link,  which 
rocks  on  a  fulcrum  pin  which  does  not  pass  through  the  centre, 
and  so  leaves  the  curved  slot  in  it  clear  for  the  traverse  of  a  die 
on  the  end  of  the  radius  rod  E. 

From  the  cross  head  descends  a  fixed  arm  F,  which. is  united 
to  the  floating  lever  G  by  a  link.  The  upper  end  of  G  swings 
on  a  pivot  J,  in  an  extension  I  of  the  valve  spindle  H. 

The  leading  end  of  E  is  pivoted  to  G,  about  3J  inches  under 
J.  The  floating  lever  is  carried  by  I,  which  moves,  as  shown, 
in  a  long  guide.  The  dotted  lines  show  various  positions  of 
D  as  the  driving  wheels  revolve.  L  is  a  bell-crank  lever, 
worked  from  the  footplate,  which  shifts  E  up  and  down.  It 
is  clear  that,  as  has  been  explained,  the  movement  of  H  will 
be  a  compound  of  that  of  F — otherwise  the  piston — and  D.  For 
let  us  suppose  that  C  is  disconnected,  and  the  link  D  held  fast, 
then  let  the  piston  make  its  stroke  ;  G  turning  then  on  the  pin 
in  the  end  of  E  as  a  fulcrum  would  move  the  slide  valve  in  an 
opposite  direction  to  the  motion  of  the  piston.  Or  let  the  connecting 
rod  be  taken  down,  and  the  piston  held  fast  while  the  crank 
shaft  was  revolved ;  then  as  D  rocked,  G  would  turn  on  the  pin 
at  its  lower  end  as  a  centre,  and  the  slide  valve  would  be  pushed 
backwards  and  forwards  through  a  slightly  greater  distance  than 
the  travel  of  the  link. 

In  the  engine  shown  the  stroke  of  the  cross  head  is 
25T3g  inches.  The  diameter  of  the  circle  described  by  the 


232 


THE  KAIL  WAY  LOCOMOTIVE 


WALSCHAEET'S  AND   JOY'S  GEAES  233 

counter  crank  pin  is  7|  J  inches.  The  long  arm  of  the  floating 
lever  is  29JJ  inches  between  centres,  and  the  short  arm  is 
83^  inches.  The  radius  rod  I  is  573%  inches  long  between  centres. 

The  geometry  of  this  gear  is  very  elegant ;  but  on  the  whole  it 
is  much  more  simple  than  that  of  the  Stephenson  link,  because 
the  radius  link  D  has  no  motion  but  one  ;  it  rocks  on  a  fixed 
centre.  The  action  is  very  satisfactory,  and  it  is  not  really  more 
complex  than  other  gears. 

For  compound  locomotives  the  Walschaert  gear  is  easily  applied 
to   inside   cylinders,    a   single   excentric    being   used    for    each 
cylinder.     Thus  the  low  pres- 
sure inside  cylinders  of  Fig. 
79  are  so  fitted. 

Joy's  radial  valve  gear  acts 
on  a  principle  quite  different 
from  those  just  described. 
As  has  been  stated,  a  great 
number  of  radial  gears  have 

been  invented  and  tried — this  is  the  only  one  which  has  been 
adopted  for  locomotives  to  any  extent.  It  was  invented  by  the 
late  David  Joy  many  years  ago.  Mr.  Joy  was  one  of  the  pioneers 
of  the  railway  system,  and  his  great  experience  with  locomotives 
enabled  him  to  avoid  mistakes  made  by  other  inventors  possess- 
ing less  practical  knowledge. 

Let  us  suppose  that  a  link  A  (Fig.  80),  similar  in  its  nature  to 
either  of  the  two  described  above,  is  pivoted  at  the  centre  of  its 
length  B,  but  that  it  can  be  moved  on  this  centre  by  the  arm  C 
and  rod  D,  or  held  fast  so  as  to  stand  at  different  angles. 
Further,  let  the  valve  spindle  E  be  jointed  at  one  end  to  a  long 
bar  F,  called  the  radius  rod,  a  pin  at  the  other  end  of  this  rod 
entering  the  die  G  in  the  link.  As  the  length  of  the  rod  is  equal 
to  the  radius  of  the  curve  to  which  the  slot  in  the  link  is  struck, 
it  is  clear  that  if  the  pin  is  moved  up  and  down  in  the  link  by 
the  rod  H,  while  the  link  is  held  straight  up  and  down,  no 
motion  will  be  produced  in  the  valve.  If,  however,  the  link  is 
inclined  in  either  direction  as  shown  by  the  dotted  line,  then  as 
the  pin  moves  up  and  down  in  the  slot,  the  valve  will  be  moved 


234  THE  EAILWAY  LOCOMOTIVE 

backwards  and  forwards,  and  to  reverse  the  engine  it  is  only 
necessary  to  alter  the  inclination  of  the  link.  There  is  here 
no  excentric  or  secondary  crank.  The  motion  of  the  valve  is 
caused  by  the  sliding  up  and  down  in  the  radial  link  of  the  die 
at  the  end  of  the  radius  rod  which  is  jointed  to  the  valve 
spindle. 

But  the  same  conditions  hold  for  the  Joy  radial  link  as  those 
obtaining  with  the  Stephenson  or  Walschaert  link — there  is  no 
lead.  The  objection  is  got  over,  however,  in  just  the  same  way, 
by  the  aid  of  a  floating  lever.  The  practical  application  of  the 
gear  is  shown  in  Fig.  70. 

The  links  are  heavy  steel  castings  in  one  with  a  weigh  shaft  C 
carried  in  bearings  secured  to  the  main  frames.  In  each  of 
these  is  a  hardened  die  or  rectangular  sliding  block,  curved  of 
course  to  fit  the  link  D,  and  to  this  block  is  pivoted  the  floating 
lever  E,  to  the  upper  end  of  which  is  pivoted  in  turn  the  valve 
spindle  connecting  rod.  To  alter  the  ratio  of  expansion  or  to 
reverse  the  engine  nothing  more  is  required  than  to  change  the 
angle  at  which  the  radial  link  stands,  and  this  is  done  from  the 
footplate,  through  the  bar  G,  either  with  a  lever  or  with  a  hand- 
wheel  and  screw. 

The  die  is  caused  to  move  up  and  down  by  coupling  it  with  the 
connecting  rod.  As  the  movement  of  this  rod  would  be  too 
great,  a  secondary  link  is  introduced,  as  shown  in  the  illustra- 
tion. The  angles  and  movements  are  shown  by  the  dotted  lines. 
The  geometry  of  this  gear  is  somewhat  complex  ;  it  will  be  found 
in  most  treatises  on  valve  gear. 

Joy's  gear  is  exceedingly  good,  giving  an  excellent  diagram, 
and  it  possesses  the  great  merit  that  it  permits  the  use  of  large 
inside  cylinders,  the  valve  chests  being  placed  on  the  tops  of  the 
cylinders  instead  of  between  them.  When  properly  made,  with 
large  and  well-hardened  surfaces  in  the  links  and  dies,  it  works 
with  less  friction  than  the  excentrics  of  Stephenson's  gear.  It 
is  very  easily  kept  in  order  and,  furthermore,  it  has  the  great 
merit  that  the  lead  is  constant  for  all  positions  of  the  link.  With 
the  Stephenson  link  the  lead  varies.  We  have  seen  that  it 
depends  for  its  amount  on  the  angular  advance  of  the  excentrics, 


WALSCHAERT'S  AND  JOY'S  GEAES  235 

which  instead  of  being  set  at  90  degrees  with  the  cranks  are 
usually  set  about  18  degrees  forward.  But  the  advance  of  the 
excentrics  is  virtually  settled  not  only  by  their  relations  to  the 
cranks  but  by  the  position  of  the  excentric  rod.  It  is  in  effect 
the  same  thing,  whether  we  move  the  excentric  round  on  the 
axle,  or  the  excentric  hoop  round  on  the  excentric,  the  lead  will 
be  altered  in  either  case,  but  the  place  of  the  die  in  the  Stephen- 
son  link  cannot  be  altered  without  moving  the  excentric  hoop 
round  on  the  sheave.  Both  Joy  and  Walschaert  gears  have  a 
constant  lead,  that  is  to  say,  steam  is  practically  always  admitted 
when  the  piston  is  in  the  same  position  near  the  end  of  the 
cylinder,  no  matter  when  the  cut-off  takes  place. 


CHAPTEE  XXXII 

SLIDE    VALVES 

IT  is  hoped  that  the  reader  has  now  formed  clear  ideas  as  to 
the  mode  of  action  of  the  three  types  of  valve  gear  which  are 
employed  to  the  almost  total  exclusion  of  all  others.  It  is  true 
that  modifications  are  in  limited  use ;  but  it  will  be  found  that 
these  almost  invariably  include  some  form  of  floating  lever  to  get 
lead,  while  in  others  a  species  of  combination  of  the  Joy  and 
Stephenson  links  is  made,  the  die  being  caused  to  slide  up  and 
down  in  the  link,  without  in  any  way  interfering  with  the  move- 
ment of  the  link  when  actuated  by  the  reversing  lever.  The 
consideration  of  the  advantages  sought  to  be  gained  by  improve- 
ments in  valve  gear  must  be  postponed  until  we  come  to  deal 
with  the  performance  of  locomotives  as  set  forth  by  indicator 
diagrams. 

Valve  gear  must  be  very  substantial,  with  large  and  well 
hardened  rubbing  surfaces,  because  thejwork  to  be  done  is  trying. 
The  frictional  resistance  of  a  slide  valve  does  not,  it  is  true, 
absorb  much  power  ;  but  this  is  due  to  the  circumstance  that  the 
stroke  of  a  valve  is  short.  Whether  the  stroke  is  an  inch  or  ten 
inches  affects  the  power  expended  but  in  no  way  modifies  the 
stress  to  be  overcome.  A  slide  valve  is  forced  down  on  its  seat 
by  the  pressure  on  its  back,  the  area  over  which  this  pressure  is 
exerted  being  that  of  the  exhaust  opening  in  the  valve  and 
sometimes  one  and  sometimes  two  ports  in  the  seat  according  as 
one  or  two  are  covered  by  the  valve.  The  whole  surface  of  the 
valve  is  not  to  be  taken,  because  when  metal  and  metal  are 
apparently  in  contact  there  is  always  a  thin  film  of  steam  between 
them.  A  slide  valve  suitable  for  an  18-inch  cylinder  will  have  a 
"  bridge  "  about  6  inches  X  17  inches,  representing,  say,  102 


SLIDE  VALVES  237 

square  inches,  to  which  may  be  added  the  area  of  one  port,  say 
17  inches  X  1J  inch  =  25  J,  or  a  total  in  round  numbers  of 
127  square  inches.  With  steam  at  150  Ibs.  in  the  valve  chest,  the 
total  load  carried  by  the  valve,  jamming  it  down  on  its  seat, 
would  be  19,005  Ibs.  or  over  8  tons.  What  the  co-efficient 
of  friction  is  it  is  not  easy  to  say,  because  it  varies  almost  from 
minute  to  minute  with  the  lubrication,  the  dryness  or  wetness  of 
the  steam,  and  so  on.  It  probably  varies  between  1  and  10  per 
cent.  It  is  greater  with  vertical  than  horizontal  valves.  The 
valve  gear  may  therefore  have  to  overcome  a  resistance  of  some- 
where about  1,900  Ibs.  It  is  in  no  way  remarkable  that  valve 
spindles  break  and  excentric  hoops  open  out  and  heat,  and  valves 
wear  away  rapidly.  To  appreciate  what  goes  on  it  is  necessary 
to  stand  on  the  running  board  and  watch  the  mechanism  at 
work  at  various  speeds  when  it  is  a  little  worn.  The  inexpe- 
rienced observer  will  begin  to  ask  himself  if  it  is  possible  the 
engine  can  ever  get  to  its  destination. 

Slide  valves  must  be  left  free  so  that  they  can  find  their  way 
to  their  seats.  To  this  end  they  are  always  made  with  a  rect- 
angular projection  on  their  backs,  which  fits  into  a  frame  known 
as  a  "  bridle,"  usually  forged  with  great  care  from  the  best  scrap 
iron.  Into  one  end  of  this — the  bridle  is  much  broader  than  it  is 
long — is  secured  the  valve  spindle.  As  a  rule  the  spindle  and 
the  bridle  are  now  made  in  one  piece,  but  formerly  the  bridle 
was  made  with  a  boss  into  which  the  valve  spindle  was  screwed. 

Occasionally  a  short  length  of  rod  is  provided  at  the  other  end 
of  the  bridle ;  this  passes  through  a  bush  in  the  front  of  the 
valve  chest  and  acts  as  a  guide  for  the  spindle.  There  are 
various  methods  of  supporting  the  outer  end  of  the  valve  spindle ; 
sometimes  it  is  keyed  into  a  bar,  which  has  been  turned  on  two 
centres.  The  larger  part  of  this  bar  passes  through  a  long  brass 
bush  or  cylindrical  guide  in  the  motion  plate.  The  end  of  the 
guide  rod  is  forked,  and  the  fork  embraces  the  link  and  the  die 
in  it.  A  pin  is  then  passed  through  the  two  jaws  of  the  fork  and 
the  die  block.  This  is  a  very  simple,  cheap,  and  durable  arrange- 
ment, and  has  almost  entirely  superseded  the  sling  links  which 
at  one  time  carried  the  back  ends  of  the  valve  connecting  rods. 


238  THE   EAILWAY  LOCOMOTIVE 

It  is  an  incidental  defect  in  the  mechanism  that  as  the  link 
is  always  rocking  backwards  and  forwards  the  push  and  pull  on 
the  die  are  only  momentarily  normal  to  the  valve  spindle.  The 
result  is  that  the  link  continually  tends  to  slip  the  die  up  and 
down,  and,  failing  that,  to  fly  up  and  down  on  the  die  when  the 
gear  is  at  all  worn.  The  detent  in  the  notched  arc  of  the  old- 
fashioned  lever  or  the  nut  on  the  reversing  screw  in  modern 
engines  chatters  continuously  when  the  engine  is  running.  The 
indirect  action  puts  a  heavy  stress  on  the  sling  straps  of  the 
link  and  the  guides  of  the  valve  spindles.  Little  of  this  kind 
takes  place  with  the  Walschaert  or  Joy  gear. 

Various  attempts  have  been  made  at  different  times  to  take 
some  of  the  pressure  off  the  backs  of  the  valves,  and  so  reduce 
the  stress  due  to  friction  and  prolong  the  life  of  the  valve.  We 
need  not  concern  ourselves  with  more  than  one  or  two.  The 
Richardson  balanced  valve  is  an  American  invention,  a  modifica- 
tion of  which  is  shown  in  Fig.  79.  Essentially  it  consists  of  an 
ordinary  slide  valve,  to  the  back  of  which  is  fitted  a  rectangular 
ring,  one  edge  of  which  is  seated  in  a  groove  running  round  the 
slide  valve,  while  the  other  edge  works  steamtight  on  the 
polished  inner  face  of  the  valve  chest  cover.  Sometimes  a 
circular  projection  on  the  back  of  the  slide  fits  a  ring,  the  top  of 
edge  of  which  bears  against  the  lower.  As  steam  cannot  find  its 
way  past  the  ring,  the  slide  valve  is  relieved  of  almost  all  the 
pressure  on  its  back.  This  valve,  however,  takes  up  a  great 
deal  of  room  and  can  only  be  used  when  the  slide  valves  are 
placed  directly  on  top  of  the  cylinders.  It  constitutes  an 
excellent  combination  with  Joy's  gear. 

Another  balanced  slide  valve  exhausts  directly  up  through  the 
back  of  the  valve,  which,  as  in  the  valve  just  described,  is  fitted 
with  a  balancing  ring  on  the  back.  Within  the  last  few  years 
piston  valves  have  begun  to  find  favour,  but  these  will  be  best 
dealt  with  in  connection  with  compound  and  superheated 
engines. 


OHAPTEK  XXXIII 

COMPOUNDING 

ALTHOUGH  compound  locomotives  are  not  much  in  favour  in 
this  country  they  are  in  use  on  many  European  railways,  and  to 
some  extent  in  America.  They  have  formed  a  subject  for  dis- 
cussion for  many  years,  and  it  cannot  even  now  be  said  that 
anything  like  a  universally  accepted  decision  has  been  arrived  at. 
The  reason  for  this  want  of  unanimity  will  be  understood  as  the 
reader  proceeds. 

It  has  been  already  shown  that  to  secure  economy  the  steam 
must  be  caused  to  expand  so  that  it  can  be  discharged  from  the 
cylinder  at  a  much  lower  pressure  than  that  at  which  it  entered 
it.  This  means  a  reduction  in  the  average  pressure,  and  of 
course  in  the  pulling  power  of  the  engine.  This  difficulty  could 
be  got  over  by  putting  in  larger  cylinders — that  is  to  say,  by 
augmenting  cylinder  capacity.  Although  the  average  pressure 
would  be  reduced,  the  pulling  power  of  the  cylinder  would  remain 
unchanged.  The  plan  has  been  tried  and  failed  completely  for 
reasons  which  are  worth  stating  because  they  show  some  of  the 
difficulties  which  beset  those  who  design  locomotives. 

In  the  first  place,  when  the  engine  is  starting,  full  pressure 
steam  acts  on  the  piston,  and  if  this  is  large,  then  all  the  rest  of 
the  mechanism  must  also  be  large.  Thus  a  crank  axle  big 
enough  for  a  17-inch  cylinder  will  not  suffice  for  a  19-inch 
cylinder,  and  so  on.  Consequently  a  heavy  and  expensive  engine 
results.  In  the  next  place,  the  utilization  of  the  large  cylinder 
depends  on  the  engine,  driver.  He  must  "  link  up  "  his  engine 
in  order  that  the  steam  may  be  cut  off  early  in  the  stroke  and 
expanded.  In  practice  it  has  been  found  impossible  to  get  the 
men  to  do  this.  On  inclines  they  give  their  engines  too  much 


240  THE   RAILWAY  LOCOMOTIVE 

steam,  and  the  result  is  that  they  "  ran  them  out  of  breath,"  and 
then  complain  that  the  boiler  will  not  keep  steam.  It  has  been 
proposed  to  get  over  the  difficulty  by  increasing  the  lap  from  one 
inch  to  an  inch  and  three-eighths.  Then  the  drivers  could  not 
help  using  steam  expansively,  because  do  what  they  would  the 
cut-off  would  take  place  fairly  early  in  the  stroke.  But  this  plan 
failed  because  the  engines  easily  went  blind.  Much  delay  occurred 
at  starting,  and  at  the  best  of  times  the  speed  of  the  train  rose 
too  slowly.  To  get  over  the  difficulty  it  has  been  proposed  that 
a  small  hole  should  be  bored  into  the  valve  seat  at  each  end. 
Through  this  hole,  when  the  engine  was  blinded,  steam  would 
get  in  and  start  the  engine,  and  when  speed  was  obtained,  the 
small  quantity  that  would  find  its  way  in  could  have  little  or  no 
effect  on  the  ratio  of  expansion.  In  the  United  States  the  same 
object  is  attained  by  filing  a  notch  in  the  valve  at  each  end, 
through  which  steam  enough  to  start  the  engine  could  find  its 
way.  Neither  of  these  methods  has,  however,  attained  any 
popularity.  The  problem  remains  unsolved.  Steam  was  not  used 
to  the  best  possible  advantage  in  the  locomotive. 

Then  it  was  resolved  to  try  compounding — that  is  to  say, 
using  the  steam  first  in  one  cylinder  and  then,  instead  of  turning 
it  directly  up  the  chimney,  passing  it  on  to  another  cylinder, 
precisely  as  in  marine  engines.  As  this  book  is  intended  to  be 
of  use  to  the  non-technical  as  well  as  to  the  technical  reader,  it 
is  necessary  to  explain  in  as  few  words  as  possible  what  com- 
pounding means.  For  detailed  information  the  reader  must 
consult  any  good  work  on  the  steam  engine.  It  must,  however, 
not  be  forgotten  that  the  conditions  and  limitations  under 
which  the  compound  system  can  alone  be  applied  to  the  loco- 
motive render  much  that  is  written  concerning  stationary  and 
marine  engines  inapplicable.  This  will  be  explained  more  fully 
presently. 

Let  us  suppose  that  we  have  two  cylinders  of  the  same 
diameter  side  by  side,  each  capable  of  holding  two  cubic  feet  of 
steam,  and  that  pistons  in  these  drive  two  cranks  set  at  180° 
from  each  other.  Let  the  cylinders  be  vertical,  then  when  one 
piston  is  at  the  top  the  other  will  be  at  the  bottom,  and  so  on 


COMPOUNDING  241 

alternately.  One  of  these  cylinders  is  full  of  steam,  with  the 
piston  at  the  bottom.  The  steam,  instead  of  escaping  into  the 
atmosphere,  is  now  admitted  to  the  other  cylinder  and  pressing 
on  the  piston  forces  it  down.  But  the  steam  equally  resists  the 
rising  of  the  first  piston.  The  effort  is  balanced  and  no  motion 
would  be  produced,  and  even  if  it  were  no  expansion  would  take 
place.  The  action  would  be  analogous  to  the  pouring  of  a  pint 
of  water  from  one  pint  pot  into  another. 

But  let  cylinder  number  two  be  50  per  cent,  larger  in 
diameter,  its  length  remaining  unaltered.  Instead  of  holding 
only  two  cubic  feet  it  will  now  hold  four.  Its  piston  will  have 
double  the  area.  If  the  steam  at  the  end  of  the  stroke  exerts 
5,000  Ibs.  on  the  first  piston,  it  will  exert  10,000  Ibs.  on  the 
second,  and  we  shall  have  a  net  driving  force  of  5,000  Ibs.  At 
the  end  of  the  stroke,  when  piston  number  one  has  risen  from 
the  bottom  to  the  top  of  its  cylinder  and  piston  number  two  has 
descended  to  the  bottom  of  its  cylinder  and  all  the  steam  has 
passed  from  the  first  to  the  second  "cylinder,  we  shall  have  four 
cubic  feet  of  steam  of,  say,  50  Ibs.  pressure  instead  of  two  cubic 
feet  of  100  Ibs.  pressure.  That  is  to  say,  the  steam  will  have 
been  expanded  twice ;  the  ratio  of  expansion  is  2  to  1.  Further- 
more, let  us  suppose  that  the  steam  had  been  cut  off  at  half 
stroke  in  the  first  cylinder.  Then  when  the  piston  had  com- 
pleted its  stroke  the  steam  would  have  been  expanded  twice  in 
the  first  cylinder,  that  is  to  say,  doubled  its  volume,  and  this 
steam  admitted  to  the  second  cylinder  would  at  the  end  of  the 
stroke  have  been  expanded  four  times,  because  we  had  only  one 
cubic  foot  of  it  instead  of  two  to  begin  with,  and  the  capacity  of 
the  second  cylinder  is  four  cubic  feet. 

Here  attention  must  be  called  to  an  important  fact,  namely, 
that  the  total  expansion,  no  matter  what  the  number  of  cylinders 
or  ratio  of  expansion  in  each  cylinder  may  be,  is  always  the  same 
as  though  the  expansion  had  taken  place  in  the  low  pressure 
cylinder  only.  If,  for  example,  the  capacity  of  the  low  pressure, 
that  is  the  largest,  cylinder  is  ten  cubic  feet,  and  only  one  cubic 
foot  is  admitted  to  the  high  pressure  cylinder,  then  the  ratio  of 
expansion  will  be  tenfold.  In  compound  engines  the  steam 

E.L.  R 


242  THE  EAILWAY  LOCOMOTIVE 

passes  through  two  cylinders  only.  In  triple  and  quadruple 
expansion  engines  it  passes  through  three  or  four  cylinders.  In 
every  one  of  these  cylinders  the  ratio  of  expansion  may  differ, 
but  in  the  end  it  all  comes  to  the  same  thing  as  though  the 
expansion  took  place  in  the  low  pressure  cylinder  only.  One 
practical  result  is  that  horse  power  is  calculated  on  the  basis  of 
the  average  pressure  which  should  be  attained  in  the  low 
pressure  cylinder,  all  the  other  cylinders  being  neglected.  Of 
course  it  must  be  understood  that  this  is  only  a  general  state- 
ment. Not  only  the  total  power  but  the  distribution  of  power 
among  the  cylinders  has  to  be  ascertained,  as  far  as  possible. 
This  last  should  be  the  same  for  all.  If  an  engine  with  two 
cylinders  indicates  1,000  h.p.,  then  as  nearly  as  may  be  500  ought 
to  be  obtained  from  each  cylinder.  If  three  cylinders,  then 
333  h.p.  from  each,  and  so  on. 

Now  the  form  of  engines  we  have  been  considering  is  not 
suitable  to  the  locomotive,  save  under  special  conditions.  Instead 
of  the  cranks  being  opposite  each  other  they  are  at  right  angles, 
and  consequently  when  one  cylinder  exhausts  the  other  is  not 
ready  to  accept  the  steam.  The  difficulty  is  got  over  by  work- 
ing each  cylinder  as  though  the  other  did  not  exist.  The  high 
pressure  cylinder  exhausts  into  a  vessel  known  as  the  "  inter- 
mediate receiver,"  from  which  the  second  or  low  pressure 
cylinder  draws  its  supply. 

Lastly,  instead  of  using  two  cylinders,  one  twice  as  big  as  the 
other,  we  may  use  three  cylinders  all  the  same  size,  the  steam 
exhausting  from  one  cylinder  into  two  instead  of  into  one  of 
double  the  size  ;  or,  conversely,  we  may  use  two  small  cylinders 
exhausting  into  one  large  one.  All  these  methods  are  used  in 
daily  practice.  The  first  compound  locomotives  put  into  regular 
use  were  invented  by  the  late  Mr.  Francis  Webb,  Chief 
Mechanical  Engineer  of  the  London  &  North  Western  Eailway. 
They  had  two  small  outside  cylinders,  fitted  with  Joy's  valve 
gear,  which  drove  one  pair  of  driving  wheels,  and  one  large 
inside  cylinder  which  turned  another  pair  of  driving  wheels. 
The  two  high  pressure  cylinders  supplied  the  single  low  pressure 
cylinder,  which  exhausted  in  the  usual  way  up  the  chimney. 


COMPOUNDING  243 

Mr.  Webb  was  followed  by  Mr.  James  Worsdell  on  the  Great 
Eastern  Eailway  first,  and  then  on  the  North  Eastern,  who  used 
two  inside  cylinders  only,  one  much  larger  than  the  other. 

No  engines  are  now  made  anywhere  on  the  Webb  system. 
Before  describing  any  of  the  systems  of  compounding  in  actual 
use  it  is  necessary  to  explain  the  limitations  and  conditions 
referred  to  above,  for  these  it  is  which  determine  not  so  much 
what  is  and  is  not  possible  as  what  is  and  what  is  not  likely  to 
be  satisfactory. 

It  will  be  remembered  that  the  clear  space  between  the  main 
frames  of  a  locomotive  for  the  4  feet  8J  gauge  cannot  exceed 
4  feet  1 J  inches.  If  a  double  cylinder  compound  is  used  it  will  be 
found  that  the  small  cylinder  cannot  be  much  less  in  diameter 
than  it  would  have  been  if  one  of  a  non-compound  pair,  because 
increased  cylinder  capacity  is  essential,  and  that  cannot  be  had 
if  the  high  pressure  cylinder  is  reduced  in  volume  in  proportion 
to  the  increase  in  volume  of  the  low  pressure  cylinder.  Now  we 
have  seen  that  two  18-inch  cylinders  represent  the  most  that  can 
be  got  between  the  frames  unless  the  slide  valves  are  put  on  top 
of  them  or  underneath  them.  But  an  18-inch  high  pressure 
cylinder  requires  a  low  pressure  cylinder  about  26  inches  in 
diameter,  and  to  squeeze  this  into  4  feet  1J  inches,  keeping  their 
axes  parallel  and  in  the  same  plane,  is  not  easy.  Again,  the 
larger  pistons  weigh  more  than  the  smaller  pistons,  and  this 
entails  trouble  with  balance  weights.  In  a  word,  the  engine  is 
not  symmetrical.  For  this  and  for  other  reasons  connected  with 
the  details  of  construction,  when  two  compound  cylinders  only 
are  used  in  the  present  day,  they  are  almost  invariably  outside 
cylinders.  Plenty  of  room  is  in  this  way  got,  not  only  for  the 
valve  gear,  but  for  the  intermediate  receiver,  which  in  the  loco- 
motive takes  the  form  of  a  large  pipe  carrying  the  exhaust  steam 
from  the  first  to  the  second  cylinder.  The  pipe  is  often  coiled 
round  the  inside  of  the  smoke-box  to  get  capacity  in  the  form  of 
length,  while  the  steam  passing  through  it  is  to  some  extent 
dried  by^the  high  temperature  in  the  smoke-box. 

In  Mr.  Webb's  engines  symmetry  was  obtained,  but  the 
engines  \\ere  defective  in  various  ways.  The  large  inside 


244  THE  EAILWAY  LOCOMOTIVE 

cylinder  could  do  nothing  until  steam  reached  it  from  one  or 
other  of  the  high  pressure  cylinders.  It  followed  that  the  starting 
of  a  train  depended  on  one  cylinder  about  15  inches  diameter. 
The  consequence  was  that  heavy  trains  got  away  with  difficulty. 
Very  often  they  could  not  start  at  all  but  for  the  fact  that  the 
rear  driving  wheels  were  made  to  slip  on  the  rails,  and  so  steam 
found  its  way  to  the  large  cylinder.  At  the  best  of  times  the 
starting  effort  was  very  unequal  and  the  train  advanced  by  jerks 
under  the  intermittent  action  of  the  single  inside  cylinder- 
Passengers  did  not  like  this.  For  long  runs  the  Webb  locomo- 
tive was  fairly  successful ;  whether  it  was  or  was  not  economical 
remains  to  this  day  a  disputed  question. 

The  starting  of  trains  by  two-cylinder  compound  engines  has 
always  presented  a  difficulty,  as  only  one  cylinder  can  get  boiler 
steam,  and  if  its  crank  is  on  or  near  the  dead  point  the  engine 
will  not  move.  To  get  over  this  difficulty  a  special  valve  has  to 
be  added  which  will  admit  steam  to  the  low  pressure  valve  chest, 
the  engine  starting  non- compound,  which  valve  is  closed  subse- 
quently. But  it  would  not  be  safe  to  admit  high  pressure  steam 
to  act  on  the  large,  low  pressure  piston.  The  piston  rod  might 
be  bent  or  the  crank  axle  broken,  therefore  a  reducing  valve 
must  be  introduced,  that  is  to  say,  the  steam  has  to  lift  a  valve 
loaded  by  a  spring.  If  the  pressure  rises  too  high  in  the  low 
pressure  valve  chest,  then  there  is  not  sufficient  difference  in 
pressure  to  overcome  the  resistance  of  the  spring,  and  the  valve 
closes.  Usually  the  maximum  pressure  permitted  in  the  low 
pressure  cylinder  is  about  one- third  of  the  boiler  pressure,  say 
50  Ibs.  where  the  latter  is  150  Ibs.1 

If  the  intercepting  valve,  as  it  is  called,  is  worked  from  the 
footplate,  then  the  driver  after  he  has  started  his  train  may 
forget  it,  or  purposely  leave  it  open,  and  we  have  then  a  bad  non- 
compound  engine.  To  prevent  this  Mr.  Von  Berries,  a  German 
engineer,  invented  a  very  ingenious  automatic  intercepting 

1  In  some  recent  locomotives  the  intercepting  valve  is  not  used,  the 
parts  are  made  strong  enough  to  take  the  full  pressure.  These  engines  are 
four-cylinder  compounds,  two  high  and  two  low  pressure,  and  the  sub- 
divieion  renders  all  the  cylinders  comparatively  small. 


COMPOUNDING  245 

valve,  which  is  open  while  the  pressure  in  the  low  pressure 
valve  chest  is  below  a  certain  fixed  limit,  and  closes  of  itself 
as  soon  as  the  engine  has  fairly  started  its  train.  Joining  with 
Mr.  James  Worsdell,  they  patented  a  combination  of  the  two- 
cylinder  compound  and  the  automatic  intercepting  valve,  the 
result  being  Worsdell  and  Von  Berries'  patent  engine,  which 
with  various  modifications  has  been  extensively  used  abroad. 


CHAPTER  XXXIV 

PISTON    VALVES 

THE  modern  big  locomotive  is  about  twice  as  powerful  as  were 
its  predecessors.  The  express  engine  of  ten  years  ago  seldom 
had  more  than  1,200  feet  of  heating  surface.  The  modern 
engine  has  1,800  to  2,000  feet  in  Great  Britain,  much  more  in 
the  United  States  and  on  the  Continent.  Large  cylinder  capacity 
is  required  to  use  up  the  steam  produced  in  the  enormous  boiler. 
Engines  have  been  made  with  very  large  outside  cylinders,  but 
recently  it  has  been  deemed  advisable  to  use  four  cylinders 
instead  of  two.  Usually  these  are  arranged  side  by  side,  two 
inside  and  two  outside.  In  some  cases  the  engines  are  simple, 
in  others  compound.  An  immense  advantage  is  gained  in  that 
the  reciprocating  parts,  moving  simultaneously  in  opposite  direc- 
tions, balance  each  other,  and  no  balance  weights,  or  next  to  none, 
are  put  into  the  wheels.  The  rails  are  spared  "  hammer  blow," 
and  there  is  no  jumping  at  high  speeds.  In  the  United  States 
two  types  are  made,  one  the  invention  of  Mr.  Vauclain,  and  the 
other  the  invention  of  Mr.  Cole,  both  engineers  well  known  in 
the  American  railway  world.  The  four-cylinder  engine  has 
rapidly  grown  in  favour  with  the  demand  for  very  large  powers. 
In  Europe  locomotives  both  compound  and  non-compound  are  in 
use.  In  Great  Britain  its  adoption  has  been  more  leisurely, 
presumably  because  the  demand  for  mammoth  engines  is  not  very 
considerable.  It  would  be  out  of  place  to  consider  here  the 
various .  types  of  construction  found  on  different  lines.  The 
reader  is  referred  for  detailed  information  to  the  fine  work  "  La 
Locomotive  Actuelle,"  by  M.  Maurice  Demoulin,  published  in 
1906  by  Beringer,  Paris. 

The  slide  valve  has  already  been  dealt  with  very  fully.     It  is 


PISTON  VALVES  247 

now  time  to  speak  of  more  recent  methods  of  distribution 
rendered  necessary  by  the  increase  in  power  and  the  augmented 
pressure  peculiar  to  recent  locomotives.1 

About  thirty  years  ago  boiler  pressures  seldom  exceeded  130  Ibs. 
They  were  gradually  augmented,  however,  as  trains  became 
heavier,  until  150  Ibs.  was  reached.  Then  came  the  compound 
engines,  and  it  was  very  soon  found  that  150  Ibs.  was  not  enough 
to  get  advantage  from  compounding.  M.  de  Bousquet,  Loco- 
motive Superintendent  of  the  Chemin  de  Fer  du  Nord,  adopted 
220  Ibs.,  and  his  example  has  been  freely  followed.  It  is  not  too 
much  to  say  that  an  unbalanced  slide  valve  cannot  be  successfully 
worked  at  this  pressure  even  when  saturated  steam  is  used.  When 
the  steam  is  superheated  an  unbalanced  slide  valve  cannot  be 
used  at  all,  because  it  will  seize  on  the  seat,  and  something  must 
give  way.  The  consequence  is  that  piston  valves  are  used  for 
distribution.  Nominally  their  construction  is  exceedingly  simple, 
really  their  use  is  attended  with  certain  objections  to  overcome 
which  complications  have  been  introduced.  Probably  fifty  kinds 
of  piston  valves  have  been  invented,  and  about  half  as  many 
are  in  use.  The  differences  lie  in  constructive  details,  for  in 
principle  they  are  all  the  same,  and  it  will  suffice  to  illustrate 
the  first  piston  valve  that  attained  success  in  this  country.  It 
was  invented  by  Mr.  Smith,  of  the  North  Eastern  Eailway,  some 
ten  or  twelve  years  ago,  and  used  with  much  success  by  Mr.  J. 
Worsdell  when  Locomotive  Superintendent  of  that  line.  Cast 
with  the  cylinder  is  a  valve  chest,  shown  in  section  in  Fig.  81  by 
H.  At  each  end  of  this  chest  is  a  cylindrical  portion  L  L.  These 
cylinders  are  bored  out,  and  into  them  are  forced  by  hydraulic 
pressure  other  cylinders  or  barrels  of  specially  hard  cast  iron, 
bored  and  turned  inside  and  out.  In  these  barrels  are  cut  ports 
M  M,  as  shown  in  the  cross  section,  which  establish  communica- 
tion between  the  insides  of  the  valve  cylinders  through  chamber  C, 
and  thence  to  the  cylinder  ports  P. 

In  the  valve  cylinders  move  the  two  pistons  N  N,  secured  on 

1  It  is  very  usual  to  speak  of  the  valves  and  valve  gear  of  an  engine  taken 
as  a  whole  as  "the  system  of  steam  distribution,"  or,  more  shortly,  "the 
distributing  system." 


248 


THE   EAILWAY  LOCOMOTIVE 


the  valve  spindle  by  a  collar  and  nut.  The  pistons  are  provided 
with  packing  rings.  Steam  is  admitted  from  the  boiler  to  each 
end  of  the  valve  chest,  and  the  pressure  only  acts  to  push  the 
two  pistons  together.  They  are  therefore  balanced  and  can  be 
moved  backwards  and  forwards  each  in  its  respective  cylinder 
without  any  resistance  but  that  of  the  friction  of  the  packing 
rings  and  the  stuffing  box  for  the  valve  spindle.  Into  the  central 
chamber  opens  the  exhaust  pipe,  which  either  carries  the  steam 


il^l^-      _jr^A.Jw.v  wfflffiJmxK^-Ll^^- 


EIG.  81. — Smith's  piston  valve. 

to  the  blast  pipe  or  into  the  valve  chest  of  the  low  pressure 
cylinder,  according  as  the  engine  is  not  or  is  compound.  The 
action  is  precisely  that  of  a  slide  valve,  the  lap  being  obtained 
by  widening  the  packing  rings  as  shown. 

The  objections  to  the  piston  valve  are,  first,  that  it  takes  up  a 
great  deal  of  room  ;  secondly,  the  ports  must  be  carefully  made 
in  such  a  way  that  a  packing  ring  can  get  into  them.  This  is 
easy  enough  so  long  as  this  ring  remains  unbroken,  but  rings 
will  break,  and  if  a  portion  sticks  in  a  port,  then  disaster  is  sure 
to  follow.  Thirdly,  the  pressure  of  the  steam  acting  on  the  rings 


PISTON  VALVES  249 

when  they  are  over  the  ports  may  cause  them  to  collapse  at  each 
stroke,  when  serious  leakage  will  occur.  Fourthly,  when  water 
accumulates  in  the  cylinders,  as,  say,  when  prhning  takes  place, 
in  a  slide  valve  engine,  the  valve  lifts  off  its  seat  when  the  piston 
strikes  the  water  at  the  end  of  the  stroke  and  no  harm  is  done  ; 
but  the  water  cannot  escape  when  a  piston  valve  is  used,  and  a 
spring  loaded  relief  valve  must  be  fitted  at  each  end  of  each 
cylinder.  Fifthly,  when  steam  is  shut  off  with  a  slide  valve 
engine  the  pistons  will  act  as  a  pump  and  draw  steam  out  of 
the  steam  pipe  and  so  make  a  vacuum,  but  compression  takes 
place  at  each  end  of  the  stroke  and  lifts  the  valve  off  its  seat, 
and  air  enters  and  restores  the  equilibrium.  This  is  the  reason 
why  the  slide  valve  of  some  engines  may  be  heard  "  clattering  " 
as  a  locomotive  runs  with  steam  off  alongside  a  platform.  The 
piston  valve  cannot  do  this,  and  the  result  is  that  when  steam  is 
shut  off  the  pistons  run  against  the  full  pressure  of  the  atmo- 
sphere and  resist  the  movement  of  the  train.  To  avoid  this,  a 
special  valve  has  to  be  used  which  prevents  the  setting  up  of  a 
vacuum.  From  all  this  it  will  be  seen  that,  excellent  and  indeed 
essential  as  the  piston  valve  is,  its  use  is,  as  has  been  said  above, 
not  unattended  with  difficulties. 


CHAPTEK  XXXV 

THE    INDICATOR 

THIS  treatise  would  be  incomplete  if  it  did  not  contain  a  setting 
forth  of  some  of  the  arguments  for  and  against  the  compound 
system,  which  are  urged  with  as  much  vehemence  to-day  as  they 
were  at  any  other  period  in  the  history  of  the  locomotive. 

It  is  necessary  here  to  say  something  about  the  Indicator,  an 
instrument  which  does  for  the  engineer  very  much  what  the 
stethoscope  does  for  the  physician.  For  reasons  already  stated, 
much  in  this  book  is  intended  for  the  use  of  the  non-technical 
reader.  The  following  short  description  comes  under  this  head. 

The  pressure  of  the  steam  continually  alters  in  the  cylinder 
as  the  piston  moves.  In  order  to  ascertain  what  these  changes 
of  pressure  are,  the  indicator  is  fitted  to  each  end  of  the  cylinder. 
The  instrument  consists  of  a  very  carefully  finished  cylinder 
containing  a  piston  with  an  area  usually  of  precisely  half  a 
square  inch.  On  the  top  of  this  piston  is  fitted  a  spring  holding 
it  down.  The  piston  rod  is  jointed  to  one  arm  of  a  very  light 
parallel  motion.  The  end  of  this  arm  carries  a  blunt-pointed 
German  silver  pin  or  style,  which  can  be  swung  into  contact 
with  a  strip  of  metallic  paper  rolled  round  a  cylinder.  This 
cylinder  can  be  caused  to  rotate  through  about  seven-eighths  of 
a  circle  by  a  cord  secured  at  one  end  to  the  paper  cylinder,  at 
the  other  to  a  lever  connected  with  the  cross  head  of  the  engine. 
Steam  from  the  cylinder  gets  access  through  a  stop-cock  to  the 
cylinder  of  the  indicator.  The  piston  of  the  indicator  will  rise 
and  fall  with  the  pressure  in  the  engine  cylinder,  and  the  paper 
roll  will  rock  backwards  and  forwards.  If  now  the  style  be 
pressed  lightly  against  the  metallic  paper  on  the  roller,  a  diagram 
will  be  drawn  which  represents  all  the  pressures  in  the  engine 


THE  INDICATOR  251 

cylinder  during  one  revolution  of  the  crank  axle.  Not  only  this, 
but  it  will  tell  precisely  at  what  part  of  the  stroke  each  pressure 
was  exerted,  and  it  enables  the  performance  of  the  valve  gear  to 
be  examined.  It  tells  in  a  word  just  what  is  going  on  inside  the 
cylinder.  Furthermore,  by  drawing  ordinates  across  it  at  equal 


FIG.  82. — Thompson  indicator  with  open  spring. 

distances  and  measuring  the  length  of  these  on  a  scale  with 
which  the  indicator  spring  has  been  calibrated,  we  get  the  average 
pressure  throughout  a  stroke,  and  thence  by  a  very  simple 
calculation  we  arrive  at  the  horse  power.  Examples  of  diagrams 
will  be  given  presently. 

Fig.  82  illustrates  a  modern   indicator  of  the   highest  class 


252  THE   EAILWAY  LOCOMOTIVE 

made  by  Messrs.  Schaffer  and  Budenberg.  When  the  spring  is 
heated  it  is  weakened,  and  therefore  is  no  longer  accurate.  To 
avoid  this  the  spring  instead  of  being  put  inside  the  cylinder  is 
put  outside  it.  All  the  details  are  very  clearly  shown.  The 
piston  is  of  steel,  ground  to  fit  steamtight  and  yet  to  move 
without  friction.  Its  range  of  motion  does  not  exceed  half  an 
inch.  There  are  many  other  types  of  indicator  equally  good, 
but  the  differences  are  in  the  main  in  detail,  the  objects  had  in 
view  being  the  reduction  of  weight  in  the  primary  parts,  con- 
venience in  handling,  diminution  of  friction,  and  strength. 
There  are  various  treatises  on  the  indicator  to  which  the  student 
is  referred  for  further  information. 

Now,  the  pressure  of  any  given  weight  of  any  gas  whatever 
varies  with  its  volume.  If  we  halve  the  volume  we  double  the 
pressure.  If  we  double  the  volume  we  halve  the  pressure,  and 
so  on.  This  is  known  as  Marriotte's  law,  and  is  written 
P  Y  =  a  constant.  That  is  to  say,  the  pressure  and  the  volume 
of  any  given  weight  of  gas,  say  1  lb.,  multiplied  together, 
always  come  to  the  same  amount.  It  follows  from  all  this  that 
when  the  indicator  tells  us  what  the  pressure  is  at  any  point  in 
the  stroke  of  the  piston,  as  we  know  the  volume  occupied  by  the 
steam,  we  ought  to  be  able  to  tell  precisely  what  weight  of  steam 
has  been  admitted  to  the  cylinder.  This  holds  true  of  a  gas.  It 
does  not  hold  true  of  saturated  steam,  which  is  not  a  gas,  but,  as 
the  reader  will  remember,  a  vapour  in  a  state  of  unstable 
equilibrium.  We  can,  by  weighing  the  quantity  of  water  pumped 
into  a  boiler  in  any  fixed  period,  as,  say,  an  hour,  ascertain  pre- 
cisely what  weight  of  steam  is  supplied  to  the  engine.  If  nothing 
happened  to  this  steam,  the  P  V  =  C  law  would  apply.  In 
practice,  however,  this  is  not  the  case.  The  pressure  is  always 
less  than  it  ought  to  be ;  in  other  words,  the  indicator  does  not 
account  for  all  the  water  pumped  into  the  boiler.  There  are 
various  sources  of  loss.  Thus  the  slide  valves  or  the  piston  may 
leak ;  or  part  of  the  feed  water  was  not  evaporated  at  all,  but 
came  over  as  priming.  But  the  principal  loss  is  due  to  conden- 
sation, and  that  condensation  is  in  its  turn  due  to  the  varying 
temperatures  inside  the  cylinder.  The  inner  surface  of  it  is 


THE   INDICATOE  253 

first  heated  up  to,  say,  380°  F.,  which  is  approximately  the  tem- 
perature of  200  Ibs.  steam — 185  Ibs.  safety-valve  load — when 
the  admission  port  opens.  Then  it  falls  gradually  as  the  pressure 
falls  during  expansion,  and  after  the  exhaust  port  has  opened  the 
temperature  of  the  vapour  remaining  in  the  cylinder  is  little 
ahove  212°  F.  It  will  be  seen,  therefore,  that  the  insides  of  the 
cylinder  covers  and  the  two  piston  faces  are  submitted  to  a  range 
of  temperature  of  380° -212°=  168°  F.  It  would  be  impossible 
to  go  here  into  the  intricate  theory  of  heat  exchanges  in  the 
cylinder  walls,  as  worked  out  by  many  English,  French,  and 
Belgian  engineers.  It  is  enough  to  say  that  "  initial  condensa- 
tion " — that  is  to  say,  the  condensation  of  the  first  steam  that 
enters  the  cylinder  and  parts  with  its  heat  to  warm  up  the 
cylinder  and  piston  at  the  commencement  of  each  stroke — has 
long  been  recognised  as  a  source  of  loss.  As  much  as  30  per 
cent,  of  all  the  steam  supplied  to  a  cylinder  may  be  turned  into 
water  in  it  and  do  no  work,  representing  a  waste  of  30  per  cent,  of 
the  coal  burned. 

Condensation  is  also  caused  by  radiation  from  the  outside  and 
conduction.  The  cylinder  is  cooled  down  by  the  air  through 
which  it  passes.  Heat  is  conducted  through  its  walls  to  the  side 
frames,  and  so  on.  The  student  of  thermodynamics  knows  also 
that  liquefaction  takes  place  because  part  of  the  heat  of  the  steam 
is  converted  into  work.  The  first  and  most  obvious  remedy  is  to 
keep  the  cylinder  hot ;  the  second  is  based  on  a  theory  which 
now  claims  explanation. 

In  a  general  way  it  may  be  said  that  the  weight  of  steam  con- 
densed in  a  given  time  by  a  given  metallic  surface  varies  chiefly 
as  the  difference  in  temperature.  If,  for  example,  30  per  cent, 
represented  the  condensation  when  the  limits  of  temperature 
were  168°  F.,  then  15  per  cent,  would  be  liquefied  if  the  limits 
were  84°  F.,  and  so  on.  It  is  on  this  fact  that  the  whole  theory 
— which  must  not  be  confounded  with  practice — of  the  compound 
engine  is  based.  It  will  be  readily  understood  that  if  the  pressure 
in  a  cylinder  is  not  permitted  to  drop  too  far  the  condensation 
ought  to  be  reduced.  We  have  seen  that  the  range  may  be  168° 
in  a  single  cylinder,  but  in  a  compound  engine  the  range  in  the 


254  THE  EAILWAY  LOCOMOTIVE 

first  cylinder  might  be  only  52°,  the  pressure  falling  from 
200  Ibs.  to  100  Ibs. ;  while  in  the  low  pressure  or  second  cylinder 
the  range  would  be  106°,  answering  to  100  Ibs.  pressure  and 
atmospheric  pressure.  The  range  of  temperature  in  any  one 
cylinder  being  lowered  in  a  very  obvious  way,  it  is  claimed  that 
condensation  is  greatly  reduced. 

It  may  be  safely  said  that  the  soundness  of  this  theory  has 
never  been  universally  accepted.  In  the  first  place  it  is  clear 
that  although  the  range  of  temperature  in  any  one  cylinder  is 
diminished,  yet  that  the  total  weight  of  metal  to  be  heated  and 
cooled  at  each  stroke — or,  in  other  words,  the  condensing  surface 
in  the  engine — is  much  increased.  Again,  in  practice,  it  is  found 
that  the  percentage  liquefied  is  about  the  same  in  a  compound  as 
it  is  in  a  simple  engine.  Into  the  general  reasons  why  the  compound 
engine  is  more  economical  than  the  simple  or  non-compound 
engine  it  would  be  impossible  to  go  here.  We  are  dealing  with 
locomotives,  not  with  engines  in  general,  and  the  compound 
locomotive  will  be  more  economical  than  the  simple  engine 
almost  entirely  because  the  cylinder  capacity  is  augmented, 
while  the  objections  already  explained  to  cutting  off  early  in  a 
single  large  cylinder  are  avoided.  Thus  a  compound  locomotive 
property  designed  will  not  under  any  circumstances  "  go  blind." 
Furthermore,  even  at  low  velocities,  the  steam  is  worked  expan- 
sively of  necessity.  The  driver  cannot  help  himself.  Now 
locomotives  as  a  rule  run  slowly  only  when  pulling  heavy  trains, 
and  when  running  slowly,  if  they  are  put  into  full  gear  forward, 
the  steam  leaves  the  cylinder  at  a  very  high  pressure,  and  with 
much  work  still  in  it.  Any  reader  who  has  stood  beside  a  steep 
incline  and  heard  a  locomotive  pulling  a  train  up  it  will  realise 
this.  The  tremendous  noise  of  the  exhaust  tells  its  own  story  ; 
a  compound  engine  pulling  the  same  load  up  the  same  incline 
would  be  comparatively  silent.  When,  however,  the  speed  is  high 
the  conditions  are  altered.  Automatic  expansion  then  takes 
place.  The  steam  cannot  follow  up  the  piston  fast  enough 
through  the  ports.  The  diagrams  given  here  tell  the  whole 
story. 

As  it  is  essential  that  the  arguments  should  be  fully  understood 


THE  INDICATOR 


255 


a  certain  amount  of  repetition  is  necessary.  What  expansion 
means  has  already  been  clearly  explained  in  Chapter  XXIX. 
Those  who  have  read  with  care  what  has  been  said  about  lap 
and  lead  and  the  link  motion  will  remember  that  one  dis- 
tinctive feature  of  all  valve  gears  worked  by  a  link  or  its 
equivalent  is  that  by  shifting  the  link  we  can  shorten  the 


Steam  Chest  Pres.  135.  Speed  II. 

Revs. per min.  47-4-1.          Cutoff  75% 

Gradient  I  in  2G4  up.      Total  I. H. P.   370-S3. 


A. P.  74-8 


A,  R  57-20 


Steam  Chest  Pres.  I3O  Speed  30. 

Revs. per  min  129-3.  Cut  off  33 % 

Gradient  I  in  264-  up.     Total  l.H.f?  SOI  -75 


A.R  32-4-0 


Steam  Chest  Pres. 14-0.        Speed  12. 
Revs. per  min.  51-7.  Cub  off  33% 

Gradient  I  in  264  up.     Total  /.//.  P.  262  -39 

FIG.  83. 


Steam  Chest  Pres.  135. 
Revs. per  min.  280-15 
Gradient  I  in  264  down. 


Speed  65 
Cut  off  27% 
Total  l.H.P.  615-73 


stroke  of  the  valve,  and  therefore  open  less  and  less  of 
the  steam  port  as  the  point  of  cut-off  becomes  earlier.  The 
result  is  wire  drawing.  The  steam  has  to  get  in  through  so  small 
an  opening  that  it  cannot  follow  up  the  piston  moving  at  a  high 
velocity,  and  the  pressure  rapidly  falls  throughout  the  stroke, 
indeed  it  is  found  that  this  takes  place  even  if  the  valve  motion 
is  kept  in  full  gear  as  the  speed  of  the  train  augments.  The 
result  is  that,  whether  the  driver  likes  it  or  not,  the  steam  will  be 
expanded  automatically.  As  an  example  of  this,  four  diagrams 


256  THE  EAILWAY  LOCOMOTIVE 

are  given,  Fig.  83,  taken  from  an  engine  working  a  fast  passenger 
train.  The  first  was  taken  just  as  the  train  started,  in  full  gear. 
The  steam  was  admitted  over  three-fourths  of  the  stroke;  the  valve 
closed  at  A  ;  the  exhaust  port  opened  at  B  ;  the  curve  at  C  in  the 
exhaust  line  was  due  to  the  opening  of  the  exhaust  in  the  other 
cylinder  and  a  consequent  rise  in  the  blast-pipe  pressure.  In  the 
second  diagram  the  speed  had  risen  to  twelve  miles  an  hour ;  the 
engine  had  been  linked  up  and  the  cut-off  took  place  at  one-third 
of  the  stroke.  Compare  now  this  diagram  with  No.  3.  The 
position  of  the  link  has  not  been  changed,  but  the  speed  has 
risen  to  thirty  miles  an  hour,  and  we  find  pronounced  evidence 
of  wire  drawing.  The  whole  diagram  is  much  leaner  than 
No.  2.  The  precise  point  where  the  steam  port  closed  can  no 
longer  be  defined.  In  No.  4  all  this  becomes  still  more  strongly 
marked.  It  is  true  that  the  link  has  been  raised  a  little,  but  the 
speed  is  now  sixty-five  miles  an  hour,  and  the  steam  is  quite 
unable  to  follow  up  the  piston.  It  is  particularly  to  be  noted 
that  the  terminal  pressure  has  now  fallen  practically  to  that  of 
the  atmosphere.  There  is  no  more  work  left  in  the  steam  ;  it  has 
to  be  pushed  out  by  the  piston. 

Now  the  great  utility  of  compounding,  as  far  as  a  locomotive  is 
concerned,  lies  in  sending  no  steam  up  the  chimney  with  available 
work  in  it.  No  compound  engine  could  do  this  more  effectively 
than  it  is  done  in  No.  4.  But  going  to  No.  1  we  see  that  the 
steam  escaped  from  the  cylinder  with  a  pressure  of  at  least 
100  Ibs.,  and  this  was  unavoidable  under  the  conditions.  If, 
now,  a  low  pressure  cylinder  had  been  added,  in  which  this  other- 
wise wasted  steam  could  have  been  utilised,  a  considerable 
economy  would  have  resulted.  Here  we  have  in  a  nut-shell  the 
essence  of  the  whole  problem.  When  the  speeds  are  high 
the  exhaust  pressure  must  be  low;  when  the  speeds  are  low 
the  exhaust  pressure  may  be  very  high,  unless  the  engine  is 
compound.  The  slow-speed  goods  or  mineral  engine  may  be 
made  compound  with  great  advantage,  while  nothing  whatever 
might  be  gained  by  compounding  the  fast  passenger  engine. 

The  position  then  is  this  :  When  the  speeds  are  low  and  the 
loads  are  heavy  the  compound  engine  has  beyond  doubt  a 


THE   INDICATOR  257 

possible  advantage,  much  depending,  however,  on  the  way  in 
which  the  engine  is  handled.  At  high  speeds  the  compound 
engine  is  worse  than  the  simple  engine.  It  cannot  take  any 
more  work  out  of  the  steam,  the  terminal  pressures  heing  about 
the  same.  The  back  pressure  resistance  is  augmented  because 
the  piston  area  is  greater  ;  and  the  engine  is  heavier,  more 
expensive  to  make  and  to  maintain.  In  this  country  the  com- 
pound engine  has  not  achieved  much  popularity,  because  the 
working  conditions  are  not  favourable.  Abroad,  where  the  roads 
are  more  trying,  the  speeds  low,  and  the  loads  heavier,  the  system 
does  excellent  service  and  enjoys  favour.  But,  as  has  been 
.already  said,  it  does  not  appear  that  the  loss  by  condensation  in 
the  cylinders  is  sensibly  reduced,  and  it  is  a  suggestive  fact  that 
it  is  claimed  that  superheating  does  more  good  with  compound 
than  with  simple  engines,  which  could  not  well  be  the  case  if 
cylinder  condensation  did  not  remain  an  important  factor. 

Proofs  exist  in  abundance  that  the  economy  of  the  compound 
system  only  becomes  apparent  when  the  speeds  are  so  low  that 
the  terminal  pressures  in  the  cylinders  are  high.  That  is  to 
say,  it  is  not  of  use  in  passenger  locomotives.  A  crucial  experi- 
ment was  carried  out  some  months  ago  by  Mr.  Ivatt  on  the  Great 
Northern  Railway.  He  communicated  the  facts  last  year  to  the 
Institution  of  Mechanical  Engineers.  The  table  on  page  258  is 
reproduced  from  the  Transactions  of  the  Institution.  It  is  full  of 
valuable  information.  It  will  be  understood  that  three  modern 
engines  of  great  power  were  used.  No.  1300  is  a  four-cylinder 
compound,  No.  292  is  a  four-cylinder  locomotive,  which  can  be 
worked  either  compound  or  simple,  and  No.  294  is  a  two-cylinder 
simple  engine.  They  are  all  of  the  4 — 4 — 2  type,  with  almost 
identical  boilers,  the  heating  surface  being  approximately  2,350 
square  feet,  the  grate  area  in  each  being  31  square  feet. 

The  trials  from  London  to  Doncaster  were  so  arranged  that 
each  driver  and  fireman,  of  the  three  sets 'of  men  selected,  should 
run  each  engine  for  three  weeks  with  the  same  group  of  trains 
(mostly  express)  in  regular  rotation.  By  this  means  it  was 
intended  that  each  driver  should  make  the  same  number  of  trips 
with  each  engine  on  each  train,  thereby  eliminating  the  personal 

B.L.  s 


258 


THE  EAILWAY  LOCOMOTIVE 


equation  and  equalizing  all  conditions  as  far  as  possible.     The 
drivers  and  firemen  took  great  interest  in  the  trials,  and,  as  an 

RESULTS  or  TRIALS. 


Engine 
No.  1300. 
4-cylinder 
Compound. 

Engine 
No.  292. 
4-cylinder 
Combined. 

Engine 
No.  294. 
2-cylinder 
Simple. 

Miles  run,  engine        .         .         . 
,,          train  .... 
Speed,  average,  miles  per  hour   . 
Weight  of  train,  average,  tons    . 

11,286 
11,045 
49-02 

229-98 

11,670 
11,415 
49-9 
238-03 

11,673 
11,415 
49-58 
234-29 

TON-MILES  :  — 
Total  train        .... 
Including  engine  and  tender   . 
Per  hour           ,  ,                 ,  , 

2,540,130 
3,803,030 
16,759 

2,717,112-5 
3,993,812 
17,337 

2,674,420 
3,949,110 
17,030 

COAL  USED  :  — 
Per  engine-mile       .         .    Ibs. 
Per  train-mile      ;,    •,         .      ,, 
Per  ton-mile   .         .               ,, 

4486 
45-84 
0-133 

43-02 
43-98 
0-126 

44-31 
45-31 
0-131 

OIL  USED  :  — 
Per  100  engine-miles       .  pints 
Per  100  ton-miles    .               ,, 

7-34 
0-022 

7-18 
0-021 

6-22 
0-0184 

OIL  USED  :  — 
Per  100  engine-miles       .  pints 
Per  100  ton-miles    .               ,, 

7-34 
0-022 

7-18 
0-021 

6-22 
0-0184 

COSTS  :  — 
Coal— 
Per  engine-mile       .          pence 
Per  ton-mile    .         .         .    ,, 

2-4 
0-0071 

2-3 
0-0067 

2-37 
0-007 

Oil— 
Per  engine-mile       .         .    ,  , 
Per  ton  -mile    .         .         .    ,, 

0-165 
0-00049 

0-16 
0-00047 

0-14 
0-00041 

Repairs  — 
Per  engine-mile       .         .    ,, 
Per  ton-mile    .         .         .    ,, 

0-56 
0-0017 

0-45 
0-0013 

0-37 
0-001 

Total— 
Per  engine-mile       .         .    ,, 
Per  ton-mile    .         .         .    ,, 

3-125 
0-0092 

2-91 

0-0085 

2-88 
0-0085 

additional  stimulant  for  them  to  make  each  engine  show  to  the 
best  advantage,  prizes  were  arranged  based  on  the  aggregate 
performance  of  the  men,  and  not  on  that  of  any  engine.  The  men 


THE  INDICATOE  259 

ran  each  of  the  engines  for  one  week  prior  to  commencing  each 
three  weeks'  trial,  in  order  to  get  thoroughly  familiar  with 
them. 

The  engines  were  put  into  the  same  condition  of  repair  before 
the  trials,  and  were  treated  in  the  same  way  throughout,  and 
were  supplied  with  the  same  quality  of  coal,  namely,  Yorkshire 
from  the  Barnsley  bed.  Careful  account  was  taken  of  coal  and 
oil  used,  time  lost  or  made  up,  state  of  weather,  weight  and  com- 
position of  trains,  and  cost  of  running  repairs.  An  inspector 
rode  with  each  engine  during  the  trials. 

All  three  engines  drew  all  the  trains  in  turn.  The  fastest  was 
timed  at  51 '28  miles  an  hour,  and  the  other  two  at  47*16  and 
46*11  respectively.  The  average  speed  was  48'15  miles  an  hour. 
It  will  be  seen  that  the  combined  engine  had  rather  the  smallest 
coal  consumption  per  train-mile,  while  for  repairs  the  simple 
engine  came  out  best.  The  most  telling  fact  is,  however,  that 
the  total  cost  per  ton-mile  of  the  compound  engine  was  greater 
than  that  of  either  of  the  other  two. 

It  has  been  explained  in  a  preceding  page  that  an  intercepting 
valve  is  generally  used  to  reduce  the  pressure  where  steam  has 
to  be  admitted  directly  Lo  the  low  pressure  cylinder  of  a  com- 
pound engine,  as  at  starting — to  reduce  the  pressure  to  a  limit 
which  shall  be  safe  on  the  large  piston.  Mr.  Ivatt  has  taken 
advantage  of  the  small  size  of  each  piston,  when  four  are  used, 
to  dispense  with  the  reducing  valve  in  the  combined  engine 
No.  292.  The  low  pressure  inside  cylinders  have  one  valve  chest 
in  common,  and  are  16  inches  diameter  by  26  inches  stroke.  The 
two  high  pressure  cylinders  are  outside,  13  inches  diameter  by 
20  inches  stroke.  A  change  valve  is  provided,  which,  in  one 
position,  allows  full  boiler  pressure  steam  to  enter  the  low 
pressure  valve  chest  as  well  as  the  two  high  pressure  valve  chests 
outside,  and  at  the  same  time  puts  the  high  pressure  exhaust  in 
communication  with  the  blast  pipe.  The  low  pressure  exhaust 
of  course  always  goes  up  the  blast  pipe.  When  the  valve  is  in  the 
other  position  (compound)  it  cuts  the  live  steam  off  the  low 
pressure  chest  and  changes  the  exhaust  from  the  high  pressure 
cylinders  to  the  low  pressure  steam  chest.  When  the  valve 

s2 


260  THE  EAILWAY  LOCOMOTIVE 

stands  in  the  "  simple  "  position  the  engine  works  as  a  four- 
cylinder  simple,  and  the  driver  notches  up  both  reversing  gears 
accordingly.  All  the  parts  are  strong  enough  to  stand  this,  and 
that  is  the  way  the  engine  would  run  when  working  a  coal  train 
or  a  slow  heavy  goods.  In  working  a  passenger  train — say  out 
of  King's  Cross — the  engine  starts  as  a  four-cylinder  simple,  and, 
if  the  train  is  heavy,  keeps  like  that  until  the  speed  gets  up  to,  say, 
40  miles  an  hour  somewhere  about  Finsbury  Park.  Then  the 
driver  shifts  the  change  valve  and  makes  her  into  a  compound, 
puts  the  low  pressure  reversing  lever  nearly  full  over,  and  does 
his  notching  up  with  the  high  pressure  reversing  lever.  The 
result  is,  of  course,  a  very  useful  all-round  engine. 

Various  systems  of  superheating  have  been  described. 
According  to  the  late  Professor  J.  Macquorn  Rankine,  if  steam 
is  superheated  about  40°  F.  it  acquires,  as  has  been  already 
stated,  the  properties  of  a  gas.  In  other  words,  it  loses  some  of 
its  instability.  But  much  more  than  this  is  required  to  do  any 
good,  and  steam  is  superheated  in  locomotives  by  from  200°  to 
over  400°.  Thus  steam  of  380°  acquires  a  temperature  of  580° 
to  700°.  Unfortunately,  it  is  not  possible  to  secure  more  than 
an  approximation  to  regularity  of  temperature.  Care  is  taken 
as  far  as  possible  to  make  it  certain  that  no  condensation  will 
take  place  in  the  cylinders.  The  steam  then  behaves  as  a  gas 
and  the  indicator  will,  in  theory  at  least,  account  for  all  the 
water  put  into  the  boiler. 

It  does  not  require  much  knowledge  of  machinery  to  see  that 
suri'aces  heated  nearly  red  hot — iron  begins  to  glow  in  the  dark 
at  about  800° — are  liable  to  work  on  each  other  with  much 
friction.  But  the  pressure  holding  two  surfaces  together  is  an 
important  factor.  It  is  for  this  among  other  reasons  that  super- 
heated steam  cannot,  as  already  stated,  be  worked  in  engines 
with  unrelieved  or  unbalanced  slide  valves  ;  piston  valves  are 
essential.  Again,  no  vegetable  oil  can  be  used  as  a  lubricant. 
It  would  be  carbonised  at  once,  and  the  statement  is  true,  though 
to  a  less  extent,  of  animal  oils.  We  are  driven,  therefore,  to  the 
mineral  heavy  oils,  and  these  have  now  been  brought  to  very 
great  perfection  as  lubricants  for  engines  using  superheated 


THE  INDICATOR  261 

steam.  It  is  indeed  doubtful  if  very  hot  steam  could  have  been 
used  at  all  without  the  aid  of  mineral  oil. 

An  energetic  controversy  has  proceeded  for  some  time  among 
Continental  engineers  as  to  the  relative  merits  of  compounding 
and  superheating.  On  the  one  side  it  is  held  that  the  loss  by 
internal  condensation  in  the  compound  engine  is  very  small, 
and  that  the  great  increase  in  cylinder  capacity  secured  by  it  is  of 
immense  advantage  in  that  the  tractive  power  of  the  engine  can 
be  augmented  to  anything  desired  within  the  limits  of  adhesion, 
simply  by  using  the  intercepting  valve  and  working  non-com- 
pound when  necessary.  The  speed  will,  of  course,  be  slow  and 
the  boiler  able  to  supply  the  demand.  It  may  be  taken  that  the 
total  capacity  of  the  cylinders  of  a  compound  engine  is  not  less 
tban  one  half  greater  than  that  of  a  simple  engine.  If  then  the 
engine  is  worked  non-compound  it  can  utilize  three  pairs  of  driving 
wheels,  while  a  similar  simple  engine  could  only  utilize  two  pairs. 
The  argument  must  be  taken  for  what  it  is  worth.  Back  pressure 
in  the  high  pressure  cylinder  has  to  be  considered,  and  the  admis- 
sion of  steam  of  full  boiler  pressure  to  the  low  pressure  cylinder 
does  not  seem  to  be  good  practice.  The  most  that  need  be  con- 
ceded is  that  compound  locomotives  properly  handled  start  trains 
very  well,  and  are  excellent  hill  climbers.  When  four  cylinders 
are  used  it  is  quite  easy  to  carry  out  compounding,  difficulties 
which  exist  with  the  two-cylinder  compound  being  avoided. 

On  the  other  hand  advocates  of  superheating  like  Herr  Garbe, 
already  quoted,  maintain  that,  the  steam  being  more  efficient,  a 
larger  cylinder  in  proportion  to  the  boiler  can  be  used  without 
risk  of  "  running  the  engine  out  of  breath,"  and  that  in  this 
way  great  tractive  effort  is  secured,  while  the  economy  attained 
is  greater  than  anything  that  can  be  had  from  compounding. 
Furthermore,  superheating  is  of  use  at  all  times  and  under  all 
conditions,  whether  the  speed  is  high  or  low,  whether  the  engine 
is  climbing  a  bank  or  running  on  a  level,  and  this  in  contra- 
distinction to  the  compound  system,  which  is  of  use  only  at  low 
velocities  when  a  "fat"  diagram  is  given  by  the  working  con- 
ditions. It  is  worth  a  passing  notice  that  both  parties  claim  a 
saving  of  about  12  per  cent,  as  compared  with  ordinary  "simple" 


262  THE  EAILWAY  LOCOMOTIVE 

engines  on  the  same  duty.  Superheating  and  compounding 
have  been  tried  in  the  same  engine,  but  no  one  claims  that  a 
saving  of  24  per  cent,  is  effected.  Indeed,  so  far  as  can  be 
learned,  the  duplicate  system  is  very  little  if  at  all  better  than 
either  of  the  two  alone.  An  advantage  is,  however,  secured,  though 
a  small  one,  by  placing  the  intermediate  receiver,  which  is  in 
point  of  fact  the  pipe  uniting  the  high  and  low  pressure  cylinders, 
in  the  smoke-box,  by  which  means  the  steam  is  dried  on  its  way 
to  the  low  pressure  cylinder. 

It  is  proper  to  observe  here  that  the  arguments  used  on  both 
sides  extend  far  beyond  what  has  been  just  stated.  Thermo- 
dynamics have  been  called  in  by  both  parties,  and  it  need  scarcely 
be  added  that  mathematical  disquisitions  abound.  These  possess 
an  academical  interest  only.  The  broad  facts  are  as  stated,  that 
compounding  may  or  may  not  be  productive  of  a  saving  in  the 
consumption  of  fuel,  according  to  the  conditions  under  which 
the  engine  is  working.  Superheating  will  certainly  give  a  saving 
in  fuel ;  but  an  efficient  superheater  is  a  very  heavy  and  very  expen- 
sive addition  to  an  engine,  and  its  life  cannot  be  long.  Let  us 
suppose  that  in  three  years  a  superheater  costing  £400  is  worn 
out.  During  that  time  the  engine  will  have  run  G0,000  miles  and 
burned  10,000  tons  of  coal.  If  we  take  the  saving  at  10  per 
cent.,  that  means  1,000  tons  of  coal.  With  coal  at  10s.  a  ton  we 
have  then  on  the  one  side  a  capital  outlay  of  £400  and  on  the  other 
a  saving  of  £500  in  coal.  Whether  superheating  should  be 
used  or  not  is  obviously  determined  by  the  price  of  coal  as  a 
principal,  though  of  course  not  the  only,  factor.  The  extra  cost 
of  a  compound  as  compared  with  a  simple  engine  is  so  small 
that  it  need  not  be  taken  into  account,  particularly  when  it  is 
remembered  that  engines  practically  never  wear  out. 

Summing  up,  it  may  be  said  that  so  far  all  the  indications  are 
that  simple  engines  will  continue  to  be  built  in  by  far  the  greater 
number  for  the  more  moderate  powers,  and  that  compounding 
and  superheating  will  both  be  used  according  to  the  proclivities 
of  locomotive  superintendents  and  the  conditions  under  which 
the  work  of  their  locomotives  is  performed. 


CHAPTEE  XXXVI 

TENDERS 

THE  tender  requires  little  description.  The  framing  is  usually 
in  all  respects  identical  with  that  of  the  engine.  In  certain  cases, 
indeed,  the  tender-wheels  axles  and  axle  boxes  are  interchange- 
able with  the  small  or  carrying  wheels  of  the  locomotive.  The 
after  part  of  a  tender  is  a  water  tank  of  thin  plate  steel,  which 
is  strengthened  by  vertical  cross  "  wash  "  plates  which  do  not  of 
course  reach  to  the  bottom.  They  are  intended  to  prevent  the 
surging  of  the  water  in  the  tank  when  the  train  is  in  motion. 
The  first  effect  of  starting  would,  for  example,  be  to  carry  all  the 
water  to  the  back  of  the  tender  for  the  moment,  and  when 
stopping  it  would  all  rush  forward.  In  front  of  the  tank  is  the 
coal  bunker.  Much  diversity  of  design  is  to  be  found  in  tenders. 
A  long,  low  tender  carried  on  six  wheels  may  be  made  very 
handsome,  bat  its  capacity  is  limited.  It  possesses  the  great 
advantage  that,  should  the  fireman  have  to  go  back  along  the 
top  to  bring  coal  forward,  his  head  will  not  strike  a  bridge. 
Fatal  accidents  have  occurred  in  this  way.  As  a  rule  the  springs 
are  in  the  present  day  always  put  outside  the  frames.  At  one 
time  they  were  often  placed  inside,  or  the  frames  were  made 
double  and  the  springs  put  between  them.  The  objection  is  that 
a  spring  may  be  broken  without  the  knowledge  of  the  driver,  or 
any  one  else,  and  that  to  replace  a  spring,  or  an  axle  box,  the 
whole  tender  having  to  be  lifted,  is  by  no  means  easy.  The 
dimensions  of  the  tender  are  partially  settled  by  that  of  the 
engine.  A  normal  tender  carries  4,000  gallons  of  water  and 
about  five  tons  of  coal.  The  water  occupies  640  cubic  feet  and 
weighs  17|  tons.  If  the  engine  uses  40  gallons  to  the  mile,  then 
4,000  gallons  will  suffice  for  100  miles.  Coal  varies  in  density. 


2fi4  THE  EAILWAY  LOCOMOTIVE 

On  a  tender  a  ton  will  occupy  about  45  cubic  feet.     The  bunker 
capacity  for  five  tons  will  therefore  be  about  225  cubic  feet. 

The  breadth  of  a  tender  is  limited,  as  is  that  of  all  rolling 
stock  on  British  railways,  by  the  width  of  tunnels  and  the  posi- 
tion of  station  platforms.  The  length  again  is  limited  in  another 
way,  namely,  by  the  diameter  of  turntables.  The  wheel  base  of 
the  engine  and  tender  together  must  not  exceed  about  50  feet. 
It  is  true  that  at  some  important  termini  the  diameter  of  turn- 
tables has  been  augmented.  But,  as  a  rale,  when  more  water 
and  coal  have  to  be  carried  than  the  quantities  stated  the 
tender  is  made  high.  Examples  of  this  may  be  seen  in  the 
very  large  tenders  in  use  for  the  express  traffic  of  the  London 
and  South  Western  Eailway,  which  are  carried  each  on  two 
four-wheeled  bogies.  In  the  United  States  enormous  tenders 
are  required  by  the  monster  engines  employed  in  the  heavy 
freight  traffic.  As  much  as  ten  tons  of  coal  are  carried  in  some 
cases. 

It  is  clear  that  to  haul  about  the  country  a  forty-ton  tender  is 
not  an  economical  thing  to  do.  Furthermore,  we  have  seen  that 
a  run  of  100  miles  is  the  limiting  distance  that  can  be  got  out  of 
4,000  gallons  of  water.  But  runs  of  considerably  over  twice  this 
distance  are  now  common.  To  accomplish  these,  the  tenders 
pick  up  water  as  they  run.  This  method  of  replenishing  tenders 
was  invented  by  Mr.  Eamsbottom  in  1857,  and  first  used  on  the 
London  and  North  Western  Railway.  Various  other  railways 
use  the  Kamsbottom  system,  modifications  being  introduced,  but 
merely  in  details.  The  system  has  been  more  fully  carried  out 
on  the  London  and  North  Western  Railway  perhaps  than  on  any 
other.  It  has  certainly  been  in  use  for  some  years,  and  attention 
may  therefore  be  confined  to  that  line. 

A  number  of  narrow  troughs  have  been  laid  down  between  the 
rails  at  convenient  places  along  the  main  lines,  which  by  an  auto- 
matic arrangement  are  kept  continually  filled  with  water,  and 
from  these  water  is  picked  up  by  the  engines  as  they  pass  over 
by  means  of  a  scoop  attached  to  the  tender.  By  this  arrange- 
ment a  train  is  enabled  to  run  from  one  end  of  the  line  to  the 
other  without  a  stop,  as  was  done  on  Sunday,  September  8th, 


TENDEES 


265 


1895,  when  a  train   left  Euston  at  8.45  a.m.  and  ran  right  to 
Carlisle  without  a  stop. 

Another  advantage  is  that  a  smaller  tender  can  be  used  than 
would  otherwise  be  required,  and  consequently  less  dead  weight. 
The  troughs  and  "pick-up"  were,  as  has  been  said,  first  intro- 
duced by  Mr.  Eamsbottom  in  1857,  and  since  then  troughs  have 


PIG.  84.— Pick-up  apparatus,  London  and  North  Western  Kail  way. 

been  laid  down  at  thirteen  different  places  on  the  main  lines. 
The  troughs  (which  are  18  inches  wide  by  6  inches  deep)  are  usually 
560  yards  long,  arid  at  each  end,  for  a  length  of  180  feet,  they  are 
gradually  reduced  in  depth,  the  bottom  of  the  trough  running 
out  at  an  inclination  of  1  in  360,  both  ends  being  open.  The 
rails  also  dip  down  at  the  same  inclination  as  the  troughs,  so  that 
by  this  arrangement  an  engine  passing  over  the  line  will,  on 
arriving  at  either  of  the  gradients,  be  gradually  lowered  until  the 


266  THE   EAILWAY  LOCOMOTIVE 


mouth  of  its  dip  pipe  is  fairly  within  the  trough,  but  not  in  con- 
tact with  the  bottom.  On  approaching  the  other  end  of  the 
trough,  the  reverse  action  takes  place,  the  engine  ascends  the 
gradient  and  gradually  withdraws  the  dip  pipe,  if  this  has  not 
previously  been  done  by  the  driver  when  the  tanks  are  filled. 

The  pick-up  apparatus,  fully  illustrated  by  the  engraving, 
Fig.  84,  is  fixed  to  the  under  side  of  the  tender,  and  consists  of 
a  dip  pipe,  the  upper  end  of  which  is  secured  to  the  bottom  of 
the  tank.  To  its  lower  end  is  attached  a  scoop,  pivoted  at  its 
sides  to  the  dip  pipe,  its  mouth  being  curved  forward  so  as  to 
meet  the  water  when  lowered  into  the  troughs  between  the  rails. 

On  the  end  of  the  pivot  on  which  the  scoop  turns  a  lever  is 
fixed,  which  is  connected  by  a  rod  to  the  engine  footplate.  The 
normal  position  of  the  scoop  is  horizontal,  with  its  mouth  clear 
of  the  troughs  and  ballast,  and  when  it  is  necessary  to  pick  up 
water,  on  approaching  the  troughs,  the  driver,  by  pulling  the  rod 
mentioned  above,  turns  the  scoop  so  that  its  mouth  is  lowered 
below  the  level  of  the  water  in  the  troughs,  which  it  scoops  up 
and  delivers  into  the  tender  tank.  As  soon  as  there  is  sufficient 
water  in  the  tank,  the  driver  pushes  back  the  rod  to  its  former 
position,  lifting  the  mouth  of  the  scoop  out  of  the  water.  Inside 
the  tender  tank,  and  immediately  above  the  dip  pipe,  another 
pipe  is  fixed,  which  forms  a  continuation  of  the  dip  pipe.  The 
top  of  this  pipe  is  continued  above  the  highest  water  level,  and 
is  then  bent  or  curved  downwards  so  that  the  water  after  passing 
up  the  dip  pipe  is  directed  into  the  tank.  The  principle  of  the 
pick-up  consists  of  taking  advantage  of  the  height  to  which 
water  rises  in  a  tube  when  a  given  velocity  is  imparted  to  it  in 
entering  the  bottom  of  the  tube,  the  converse  operation  being 
carried  out  in  this  case — the  water  being  stationary  and  the  tube 
moving  through  it.  On  the  London  and  North  Western  Eailway 
the  scoop  is  raised  and  lowered  by  a  double-threaded  screw  on 
the  tender.  On  other  lines  a  piston  in  a  cylinder  worked  by 
compressed  air  from  the  continuous  brake  is  emplo}red.  Others 
use  a  small  steam  cylinder. 

The  work  of  refilling  a  tender  tank  is  done  at  a  pace  which  is 
not  easy  to  realise.  Taking  the  length  of  the  trough  at  1,680  feet 


TENDEES  267 

and  the  speed  of  the  train  60  miles  an  hour,  or  88  feet  per 
second,  the  length  of  the  trough  will  be  travelled  in  20  seconds. 
In  this  short  time  ten  or  twelve  tons  of  water  will  be  lifted  into 
the  tender.  Indeed,  unless  the  fireman  is  on  the  alert  to  raise 
the  scoop,  the  whole  tender  and  footplate  may  be  flooded  in  a 
cataract  of  water.  This  took  place  once,  and  the  firing  shovel 
was  washed  off  the  footplate.  How  steam  was  kept  up  with 
genuine  hand-firing  until  a  station  was  reached  where  a  shovel 
could  be  got  is  not  recorded.  The  following  list  of  the  sixteen 
troughs  on  the  London  and  North  Western  Kailway  will  probably 
interest  the  reader. 

LIST  OF  WATER  TROUGHS  ON  THE  LONDON  AND  NORTH 
WESTERN  EAILWAY. 

Between  Pinner  and  Bushey. 

,,  Wolverton  and  Castlethorpe. 

„  Rugby  and  Brinklow. 

„  Tamworth  and  Lichfield. 

,,  Whitmore  and  Madeley. 

,,  Preston  Brook  and  Moore. 

,,  Brock  and  Garstang. 

,,  Hestbank  and  Bolton-le-Sands. 

,,  Low  Gill  and  Tebay. 

,,  Waver  ton  and  Chester. 

,,  Connah's  Quay  and  Flint. 

„  Prestatyn  and  Ehyl. 

„  Llanfairfechan  and  Aber. 

„  Diggle  and  Marsden. 

„  Eccles  and  Weaste. 

,,  Halebank  and  Speke. 

It  is  by  no  means  necessary  that  the  speed  of  the  train  should 
be  60  miles  an  hour.  Indeed,  much  better  results  are  got  at 
lower  speeds,  the  water  being  less  splashed  about.  The  water 
will  rise  to  any  height,  provided  the  scoop  moves  at  a  velocity 
somewhat  in  excess  of  eight  times  the  square  root  of  the  height. 
Roughly  speaking,  the  water  has  to  be  lifted  about  9  feet ;  the 


268  THE  EAILWAY  LOCOMOTIVE 

square  root  of  9  is  3,  and  3  X  8  =  24  feet  per  second  as  the 
velocity  which  the  water  would  attain  if  it  fell  9  feet.  Now  24  feet 
per  second  is  only  16'3  miles  an  hour ;  at  60  miles  an  hour  the 
water  would  be  lifted  over  120  feet,  and  is,  indeed,  projected  into 
the  tanks  with  almost  as  much  violence  as  though  it  fell  from 
that  height.  The  adoption  of  the  trough  system,  excellent  as  it 
is,  has  been  very  slow.  There  are  drawbacks  to  it.  A  very  large 
number  of  trains — even  fast  expresses — do  not  run  more  than 
100  miles  without  a  stop.  The  troughs  are  expensive  to  lay  down, 
and  the  line  must  be  dead  level  and  quite  straight  where  they  are 
placed.  But  the  strongest  objection  to  them  is  that  in  winter 
they  must  be  kept  clear  of  ice  by  platelayers  who  drag  a  small 
plough  along  the  trough.  The  under  bodies  of  the  coach  at  the 
leading  end  of  the  train  are  splashed.  The  water  freezes  and  the 
vacuum  pipes  of  the  brake  are  coated  with  ice,  become  stiff,  and 
disconnect,  stopping  the  train.  On  other  lines  the  brake  gear  is 
sometimes  held  fast  by  ice  and  is  inoperative.  But  we  seldom 
have  frosts  sufficiently  severe  to  give  much  trouble,  and  for  long 
runs  the  scoop  is  of  course  indispensable. 

As  a  considerable  saving  of  fuel  may  be  attained  by  heating 
the  feed  water,  and  the  steaming  power  of  the  boiler  is  for  some 
ill-understood  reason  augmented  more  than  theory  denotes,  a 
pipe  is  always  carried  from  the  boiler  to  the  tender.  Through 
this  steam  can  be  passed  into  the  tender  tank  when  the  engine  is 
standing  in  a  station  or  terminus,  instead  of  being  blown  off  to 
waste  through  the  safety  valves.  But,  as  has  been  shown,  the 
temperature  at  which  an  injector  will  feed  is  comparatively  low, 
and  the  heating  of  the  water  must  not  be  pushed  too  far;  besides, 
steam  is  not  available  for  heating  the  water  when  the  engine  is 
running. 

More  than  twenty  years  ago  Mr.  Stroudley  carried  a  part  of 
the  exhaust  steam  back  to  the  tender,  and  so  raised  the  tempera- 
ture of  the  feed  water.  The  whole  of  the  steam  was  thus  treated 
in  the  tank  engines  working  the  Metropolitan  Eailway  at  a  much 
earlier  date,  not  to  heat  the  feed,  indeed,  but  prevent  the  dis- 
charge of  steam  into  the  tunnel.  There  are  objections  to  the 
putting  of  exhaust  steam  direct  into  the  water.  It  is  apt  to  carry 


TENDEKS 


269 


270  THE  EAILWAY  LOCOMOTIVE 

grease  with  it,  which  is  bad  for  a  boiler  and  may  set  up  priming. 
For  some  time  past  Mr.  Drummond  has  had  in  use  with  great 
success  the  water-heating  arrangement  shown  in  Fig.  85.  Under 
the  main  tank  is  a  subsidiary  tank,  through  which  the  water  must 
pass  on  its  way  to  the  feed  pump  or  injector.  In  this  subsidiary 
tank  are  sixty-four  tubes,  through  which  a  portion  of  the  exhaust 
steam  is  passed.  It  is  condensed,  and  the  resulting  water  drains 
away  to  the  ground.  The  feed  water  is  considerably  raised  in 
temperature.  The  whole  arrangement  is  very  simple  and  inex- 
pensive, and  gives  no  trouble ;  the  temperature  of  the  water  is, 
however,  too  high  to  permit  the  use  of  an  injector,  and  a  duplex 
donkey  pump  is  employed  to  feed  the  boiler.  The  net  saving  in 
coal  averages  about  13  per  cent.,  but  the  major  advantage  is  no 
doubt  found  in  the  fact  that  the  life  of  the  fire-box  is  prolonged, 
and  the  actual  steaming  power  of  the  boiler  is  augmented  to  a 
degree  theoretically  out  of  proportion  to  the  rise  in  temperature 
of  the  feed. 

The  connection  between  the  tender  and  the  engine  has  been 
made  the  subject  of  a  good  deal  of  invention.  Usually  there 
is  one  centre  drawbar  and  two  auxiliary  bars.  They  pull  on 
india-rubber  spring  cushions  fixed  in  a  heavy  frame  under  the 
footplate  ;  the  water  is  led  from  the  tender  to  the  injector  through 
an  india-rubber  hose  pipe  at  each  side  of  the  engine.  The  flow 
of  water  is  controlled  by  two  simple  stop  cocks,  the  handles  of 
which  are  placed  one  at  each  side  on  the  wings  of  the  coal  bunker, 
where  they  are  under  the  fireman's  hand. 


CHAPTER  XXXVII 

TANK    ENGINES 

LOCOMOTIVE  engines,  however  much  alike  in  their  general 
characteristics,  are  divided  into  two  distinct  classes,  according 
as  their  supplies  of  coal  and  water  are  or  are  not  carried  in  a 
separate  vehicle.  That  is  to  say,  we  have  tender  engines  and 
tank  engines.  The  former  are  used  for  long  distance  and  the 
latter  for  short  distance  work.  Ohviously  the  quantities  of  fuel 
and  water  needed  on  suburban  lines  are  much  less  than  those 
needed  for  long  runs.  Furthermore,  the  tank  engine  being  much 
shorter  than  an  engine  and  tender,  valuable  space  is  saved,  and 
as  the  tank  engine  runs  equally  well  backwards  or  forwards  no 
turntables  are  needed,  and  a  great  saving  in  time  is  effected. 

There  are  two  varieties  of  tank  engine  ;  in  one  the  water  is 
carried  in  a  saddle  on  top  of  the  boiler,  which  holds  500  or  600 
gallons.  Locomotives  of  this  kind  are  much  used  for  shunting 
and  yard  work.  They  are  usually  small,  and  need  not  be  con- 
sidered here.  On  page  272  is  given  a  photograph  of  a  colli- 
sion which  took  place  at  Bina,  a  station  on  the  Great  Indian 
Peninsula  Railway,  at  night  in  February,  1907.  A  mail  train 
ran  into  a  shunting  train ;  both  drivers  and  one  fireman  were 
killed.  The  photograph  is  interesting  because  it  shows  very 
clearly  the  extraordinary  way  in  which  railway  vehicles  of  all 
kinds  tend  to  mount  over  each  other  in  collisions.  The  saddle 
tank  of  the  shunting  engine  is  very  clearly  seen. 

The  tank  engines  of  importance  are  those  which  carry  their 
water  in  rectangular  tanks  at  each  side  of  the  boiler,  and  some- 
times a  third  tank  is  placed  under  the  footplate  and  coal  bunker. 
They  are,  of  course,  all  united  by  a  tube  or  tubes.  The  tanks 
generally  hold  about  1,000  gallons.  They  are  often  double,  that 


272 


THE  EAILWAY  LOCOMOTIVE 


is  to  say,  the  inner  tank  portion  is  fitted  with  an  ornamental 
casing.  Engines  of  this  kind  are  largely  used  for  working 
suburban  traffic.  They  have  gradually  augmented  in  dimensions 
until  some  of  them  are  exceedingly  powerful,  handsome  engines. 
They  have  small  driving  wheels,  often  six-coupled,  the  great 
object  in  view  being  rapid  acceleration,  so  that  they  can  get  away 
with  their  loads  from  stations  very  quickly.  They  are  seldom 


Collision  at  Bina,  Great  Indian  Peninsula  Railway. 

required  to  run  faster  than  thirty  miles  an  hour.  It  has  been 
proposed  to  construct  tank  engines  with  large  driving  wheels  and 
to  supply  them  with  water  by  scoops  in  order  to  save  the  haulage 
of  a  tender,  but  the  proposal  came  to  nothing. 

Tank  engines  in  the  present  day  are  more  often  fitted  with 
traversing  leading  or  trailing  axles  than  with  bogies.  At  one 
period  all  large  tank  engines  had  bogies  at  either  one  end  or  the 
other.  In  the  general  details  of  the  construction  they  conform 
closely  to  tender  engines,  except  that,  as  has  been  said,  they 
almost  invariably  have  wheels  under  6  feet  in  diameter. 


TANK  ENGINES  273 

The  question  of  acceleration  mentioned  above  is  one  of  the 
utmost  importance  in  working  suburban  and  metropolitan  traffic. 
To  it  is  mainly  due  the  substitution  of  electricity  for  steam  in 
cases  like  the  Liverpool  and  Southport  line,  where  ventilation 
had  nothing  to  do  with  the  matter.  Time  saving  in  the  case 
of  suburban  and  metropolitan  traffic  is  of  the  utmost  import- 
ance. On  the  Great  Eastern  Eailway  Mr.  Holden  appears  to 
have  done  all  that  can  be  done  with  steam.  Travelling  inspectors 
took  a  record  of  the  average  time  occupied  at  a  platform  from 
stop  to  start.  Over  30,000  observations  were  made.  The  average 
obtained  was  27'5  seconds.  To  consider  the  question  in  all  its 
bearings,  its  influence  upon  gradients,  as  determining  when  it  is 
and  is  not  economically  right  to  flatten  a  gradient,  and  so  on, 
would  be  impossible  here,  and  indeed  somewhat  beyond  the  scope 
of  this  book.  It  is  worth  while,  however,  to  give  an  accelerating 
formula  used  by  railway  men  in  the  United  States. 

The  resistance  due  to  acceleration  energy  of  retardation  is 
equal  to  70  (Vi2-V22)  -f-  D,  in  which  Vi  and  V2  represent  the 
initial  and  the  terminal  velocities  in  miles  per  hour,  and  D 
equals  the  distance  in  feet  travelled  in  accelerating  or  retarding 
the  velocity. 

The  distance  travelled  in  accelerating  or  retarding  speeds 
from  mile  to  mile  is  obtained  by  transposing  the  equation  for 
resistance  due  to  acceleration. 

Feet  distance  travelled  —  70  (Vi2  —  V22)  -f-  K,  where  R  equals 
the  difference  per  ton  between  power  of  engine  and  resistance  of 
train,  as  already  explained.  Whenever  the  difference  per  ton  is 
positive,  i.c,  when  the  drawbar  pull  is  in  excess  of  train  resist- 
ance, the  distance  travelled,  obtained  by  the  formula,  will 
represent  distances  travelled  in  acceleration,  while,  when  it  is 
negative,  the  distances  will  be  those  in  retardation  of  velocity.1 

A  word  of  explanation  is  desirable  here  to  render  the  curious 
experiment  illustrated  by  Figs.  86  and  87  intelligible.  In  every 
body,  no  matter  what  its  shape  is,  there  is  a  point  called  the  centre 

1  For  further  information  the  reader  is  referred  to  a  paper  by  Mr. 
A.  K.  Shurtleff,  in  the  Bulletin  of  the  American  Railway  Engineering  and 
Maintenance  of  Way  Association  for  November,  1907. 

R.L.  T 


274 


THE  RAILWAY  LOCOMOTIVE 


TANK  ENGINES 


275 


of  gravity,  such  that  if  the  body  be  suspended  from  this  point  it 
will  remain  in  equilibrium  indifferently  in  any  position  ;  and  if 


FJG.  87. — Finding  the  centre  of  gravity  of  a  tank  engine. 

the  body  be  suspended  from  any  other  point,  then  it  will  be  in 
equilibrium  when  the  centre  of  gravity  is  directly  under  the 
point  of  suspension,  and  any  vertical  line  drawn  from  any  other 


T  a 


276  THE   KAILWAY  LOCOMOTIVE 

point  of  suspension  will  pass  through  the  centre  of  gravity.  If, 
for  example,  an  irregular  figure  is  cut  out  in  cardboard  and  freely 
suspended  from  any  point,  behind  a  plumb  line,  then  a  line  can 
be  drawn  along  the  card  with  a  pencil  coincident  with  the  string. 
Next  let  the  card  be  freely  suspended  from  any  other  point  in  it 
as  before,  and  a  second  pencil  line  be  drawn  upon  it  coincident 
with  the  string,  The  second  pencil  line  will  intersect  the  first 
pencil  line,  and  the  point  of  intersection  is  the  centre  of  gravity. 
And  it  matters  nothing  how  often  the  operation  is  repeated,  the 
pencil  lines  will  all  intersect  in  the  same  place. 

As  it  is  not  always  feasible  to  hang  up  heavy  bodies  to  get 
their  centre  of  gravity,  recourse  is  had  to  calculation.  The 
weights  of  different  parts  are  taken,  and  their  moments,  that  is 
to  say  their  leverages  round  an  assumed  point,  are  taken,  and  in 
this  way  the  centre  of  gravity  is  obtained.  The  influence  of  the 
position  of  this  point  on  the  behaviour  of  an  engine  on  the  road 
has  already  been  fully  considered  in  Section  I. 

In  1905  Mr.  Aspinall  made  the  experiment  illustrated.  He 
suspended  one  of  his  large  radial  tank  engines,  in  working 
order,  with  coal  and  water,  from  the  traversing  crane  in  one  of 
the  Honvich  shops  of  the  Lancashire  and  Yorkshire  Railway. 
Two  points  of  suspension  were  selected.  On  the  back  of  the 
tank  are  shown  three  vertical  lines  drawn  by  the  aid  of  a  plumb 
line.  They  intersect,  it  will  be  seen,  and  the  point  of  inter- 
section gives  the  vertical  height  of  the  centre  of  gravity  above 
the  rails.  Calculations  which  were  previously  made  gave  the 
height  as  4  feet  10  inches,  and  the  actual  experiment  gave  it  as 
4  feet  11^  inches,  a  very  close  approximation.  The  great 
height  of  the  modern  big  boiler  engine  deceives  the  eye.  Thus 
an  engine  with  a  boiler  standing  8  feet  11  inches  above  the  rails 
will  have  a  centre  of  gravity  only  5  feet  6  inches  above  them. 

The  ordinary  observer  is  apt  to  forget  that  little  more  than 
half  the  boiler  barrel  is  filled  with  water,  and  that  the  upper  half 
therefore  contributes  very  little  weight  to  the  whole  structure. 
These  large  engines  run  with  very  much  greater  smoothness 
than  is  possible  with  an  engine  whose  centre  of  gravity  is  very 
low  down,  for  reasons  already  set  forth. 


TANK  ENGINES  277 

In  the  first  section  of  this  book  the  subject  of  derailment  has 
been  treated  on  general  principles,  and  no  reference  has  been 
made  to  the  relative  safety  of  the  two  types  of  engine,  tender  and 
tank,  for  it  appeared  that  this  question  would  be  best  postponed 
until  the  tank  engine  came  up  for  consideration.  This,  then, 
seems  the  proper  place  to  mention  a  discussion  which  took 
place  some  years  ago  between  locomotive  superintendents  and 
Board  of  Trade  inspectors.  These  gentlemen  assumed  that  the 
tank  engine  must  be  more  liable  to  derailment  than  a  tender 
engine.  Mr.  Aspinall  determined  to  ascertain  from  statistics 
whether  this  was  or  was  not  true,  and  he  had  information 
collected  from  the  Board  of  Trade  returns.  These  were  in  a 
sense  private,  and  the  author  is  indebted  to  Mr.  Aspinall  for  per- 
mission to  make  the  facts  public  here  for  the  first  time,  in  the 
shape  of  the  following  memorandum  : — 

MEMORANDUM  re  DERAILMENTS  OF  PASSENGER  TANK  ENGINES. 

The  diagram  has  been  prepared  for  the  purpose  of  illustrating 
the  reports  made  by  the  various  Board  of  Trade  inspectors  upon 
all  classes  of  tank  engines  and  all  classes  of  tender  engines  which 
have  been  derailed  during  the  twenty  years  ending  December  31, 
1904,  as  stated  in  the  return  made  to  both  Houses  of  Parliament, 
entitled  "  Eeturn  of  Cases  of  Derailment  of  Engines  of  Passenger 
Trains  during  the  twenty  years  ending  31st  December,  1904, 
divided  into  (1)  Tank  Engines,  and  (2)  Tender  Engines,  show- 
ing in  each  case  the  date,  place  of  accident  and  railway,  and  the 
class  of  engine  " ;  signed  by  Sir  Francis  Hop  wood,  and  dated 
Board  of  Trade,  May  24,  1905.  All  the  facts  and  figures  are 
takes  from  the  above  official  return. 

This  diagram,  Figs.  88  and  89,  is  divided  into  nine  parts,  which 
are  numbered  1  to  9. 

Diagram  No.  1. — This  gives  small  diagrams  showing  how  each 
type  of  tender  engine  reported  upon  is  arranged  so  far  as  wheels 
are  concerned,  and  what  class  of  tender  was  hauled  behind  the 
engine. 

Diagram  No.  2  gives  similar  information  with  regard  to  the 
wheel  arrangements  of  the  several  types  of  tank  engines. 


278 


THE  EAILWAY  LOCOMOTIVE 


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280  THE   EAILWAY  LOCOMOTIVE 

Diagram  No.  3  shows  by  means  of  a  black  line  that  the  number 
of  locomotives  which  were  possessed  by  the  different  railway 
companies  had  increased  from  15,196  in  the  year  1885  to  22,443 
in  1904 ;  and  it  also  shows  the  number  of  tender  engines  which 
were  derailed  in  each  year  by  means  of  a  dotted  line,  and  the 
number  of  tank  engine  derailments  by  means  of  a  heavy  line.  For 
example,  it  will  be  observed  from  this  diagram  that  there  were 
two  tender  engines  derailed  in  1885  and  four  tank  engines 
derailed  in  1885,  but  only  two  of  the  latter  in  1904.  This 
diagram  does  not  point  to  there  being  any  greater  tendency  for 
a  tank  to  become  derailed  than  for  a  tender  engine. 

Diagram  No.  4  is  divided  into  two  parts,  and  shows  by  the 
height  of  columns  either  lined  or  hatched  the  number  of  derail- 
ments of  tender  engines  on  the  left-hand  side,  and  of  tank 
engines  on  the  right-hand  side,  and  enables  the  different  classes 
to  be  picked  out  by  reference  to  diagrams  1  and  2,  where  the 
letters  "A,"  "B,"  "C,"  etc.,  are  applied  to  each  type  of  engine. 
For  instance,  with  tender  engines  of  class  "  C,"  with  a  leading 
bogie,  sixteen  are  shown  to  have  left  the  road  by  the  column 
which  stands  over  the  letter  "C";  in  like  manner,  with  tank 
engines  twelve  are  shown  to  have  left  the  road  by  the  column 
over  the  letter  "  A."  Those  who  are  familiar  with  the  very  large 
amount  of  work  done  upon  English  railways  by  tender  engines 
of  class  "C"  and  tank  engines  of  class  "  A  "  will  recognise  that 
it  is  only  reasonable  to  expect  that  as  these  classes  of  engines  are 
employed  most  largely,  so  the  number  of  derailments  will  be  greater 
than  in  exceptional  classes,  where  only  few  engines  are  employed. 

The  same  remarks  would  apply  to  tender  engines  of  the  "  I " 
class  and  tank  engines  of  "  L  "  class. 

Diagram  No.  5  shows  that  there  have  been  ten  cases  in  which 
the  tender  alone  has  been  derailed. 

Diagram  No.  6  shows  how  many  tender  engines  of  the  classes 
"A,"  "B,"  "C,"  etc.,  were  derailed  in  each  year. 

Diagram  No.  1  gives  details  of  the  number  of  tank  engines 
derailed  in  each  year. 

Diagram  No.  8  shows  the  total  number  of  derailments  during 
the  twenty  years  ending  December,  1904. 


TANK  ENGINES 


281 


Diagram  No.  9  shows  the  reasons  which  were  given  by  the 
different  Board  of  Trade  inspectors  as  to  why,  in  their  opinion, 
the  different  classes  of  engine  left  the  road.  It  will  be  observed 
by  looking  at  this  diagram  that  there  were  as  many  as  sixteen 
cases  of  tender  engines  and  eleven  cases  of  tank  engines  which 
are  said  to  have  left  the  road  for  reasons  connected  with  defective 
permanent  way,  including  cases  where  points  have  been  held  over 
by  stones ;  there  is  also  one  case  with  a  tender  engine,  and  one 
case  with  a  tank  engine,  where  oscillation  is  stated  to  have  been 


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6783 

igine 

SSO/    2  3  4  5  ff   789  1900  1  2  3   4 

Derailments. 

caused  by  defective  permanent  way,  but  there  is  not  a  single  case 
where  oscillation  is  said  to  have  been  caused  by  high  speed. 

The  general  effect  of  these  diagrams  is  to  show  in  the  most 
conclusive  way  that  derailments  upon  which  the  Board  of  Trade 
have  considered  it  necessary  to  make  a  report  during  a  period  of 
twenty  years  became  i'ew  in  number,  and  that  there  is  nothing 
whatever,  when  a  close  examination  of  the  reports  is  made,  to 
indicate  that  there  is  any  greater  danger  with  a  tank  engine  than 
with  a  tender  engine.  On  several  of  the  largest  railways  in  this 
country  it  has  been  found  that  no  less  than  50  per  cent,  of  their 
total  locomotive  stock  are  tank  engines,  and  that  they  run  a  large 
percentage  of  their  high-speed  passenger  mileage,  amounting  in 
one  case  to  54  per  cent.,  with  engines  of  this  class. 


CHAPTER   XXXVIII 

LUBRICATION 

IT  goes  without  saying  that  all  rubbing  surfaces  in  a  loco- 
motive engine  must  be  well  oiled.  Various  methods  of  lubrication 
are  employed.  The  first  and  most  simple  consists  in  screwing 
on  to  the  part  to  be  lubricated  a  brass  oil  cup.  Through  the 
bottom  of  the  cup  descends  a  small  brass  tube,  which  rises  nearly 
to  the  lid.  Two  or  three  strands  of  worsted,  such  as  coarse 
stockings  are  made  of,  are  put  down  the  brass  pipe  like  a  wick. 
A  bit  of  thin  copper  wire  is  twisted  in  with  them  and  hooked 
over  at  the  top  end  so  as  to  prevent  the  wick  falling  down.  It 
acts  as  a  syphon,  and  delivers  the  oil  from  the  box  drop  by  drop 
until  it  is  all  gone.  Sharp  Brothers  &  Co.,  of  the  Atlas 
Works,  Manchester,  introduced  nearly  sixty  years  ago  a  very 
elegant  system  of  lubrication.  A  long  brass  box  was  screwed  at 
each  side  to  the  boiler  near  the  smoke-box.  From  the  bottom  of 
the  box  six  or  eight  small  copper  pipes  were  led  to  the  slide  bars, 
valve  gear,  &c.  The  pipes  passed  up  through  the  bottom  of  the 
box  and  each  was  "trimmed"  with  a  wick  in  the  way  just 
described.  The  box  would  hold  a  quart  or  more  of  oil.  A  stop 
cock  was  fitted  to  each  leading  pipe  under  the  box,  by  which  the 
quantity  of  oil  distributed  to  each  bearing  was  regulated.  When 
a  trip  was  over,  or  the  engine  had  some  time  to  stand,  the  fire- 
man went  out  round  the  engine  on  the  running  board  and  closed 
all  the  cocks,  thus  effecting  a  great  saving  in  oil.  A  precisely 
similar  arrangement  is  used  in  torpedo  boats  and  indeed  on 
very  many  high-speed  engines. 

These  methods  are  not  applicable  to  what  may  be  termed 
internal  lubrication,  as,  for  example,  the  working  faces  of  slide 
valves.  To  the  late  Mr.  Ramsbottom  the  world  is  indebted  for 


LTJBKICATION 


283 


the  first  automatic  arrangement  for  oiling  valve  chests.  Fig.  90 
shows  the  luhricator  in  diagram  section.  It  consists  of  a  strong 
brass  vessel  A,  which  can  be  screwed  to  the  outside  of  the  smoke- 
box  B.  A  pipe  C  from  the  valve  chest,  fitted  with  a  three-way 
stop  cock,  comes  up  through  the  bottom  and  reaches  nearly  to 
the  top  of  the  lubricator.  E  is  a  small  brass  funnel  provided 
with  a  steamtight  screwed  plug.  Nothing  can  be  simpler.  To 
use  it  the  three-way  cock  is  turned  one  quarter  round,  until  the 
passage  G  is  vertical.  The  contents  of  A  will  then  be  dis- 
charged at  H.  The  plug  at  E  is  then  removed,  and  the  cock  D 
turned  until  all  the  passages  are  blinded.  The 
lubricator  is  then  filled  with  oil  up  to  such  a 
point  that  it  will  just  not  run  down  the  inner 
pipe.  The  filling  plug  is  then  replaced  and 
the  cock  D  is  restored  to  the  position  shown 
in  the  diagram.  As  soon  as  steam  is  turned 
into  the  valve  chest,  it  will  also  pass  through 
the  lubricating  pipe  into  the  lubricator,  filling 
the  small  empty  space  I.  It  will  there  con- 
dense, and  the  heavy  water  sinking  down 
through  the  light  oil  will  displace  the  oil, 
which  floats  on  it  and  overflows  down  through 
the  steam  cock  and  pipe  G  and  so  into  the 
valve  chest.  The  process  is  gradual,  and  by 
degrees  all  the  oil  is  displaced,  and  the  lubri- 
cator filled  with  water.  Then  the  steam  cock  is  shut  off  and  the 
drain  cock  opened.  The  water  is  run  out,  and  the  lubricator 
refilled  with  oil. 

Ingenious  and  effective  as  this  device  is,  it  is  very  defective  in 
certain  ways.  The  rate  of  discharge  from  it  depends  largely  on 
that  at  which  steam  condenses,  and  as  there  is  no  means  of 
knowing  when  the  oil  is  gone,  without  blowing  the  water 
out  of  it,  it  sometimes  happens  that  all  the  oil  disappears 
a  great  deal  too  soon.  If  the  steam  cock  is  partly  closed  to 
prevent  this,  then  the  oil  may  not  go  quickly  enough  to  the 
rubbing  surface.  In  modern  engines,  particularly  those  running 


FIG.  90. 


long 


distances,  oil  is  supplied   by  what  are   called 


sight  feed 


284  THE   RAILWAY  LOCOMOTIVE 

lubricators,  which  are  fixed  in  the  cab  under  the  driver's  eye. 
Short  lengths  of  glass  tube  are  full  of  water,  up  through  which 
the  drops  of  oil  may  be  seen  rising.  There  are,  perhaps,  fifty 
sight  feed  lubricators  in  the  market,  but  they  all  depend  for 
their  action  on  either  of  two  general  principles.  Either  the  oil 
is  supplied  under  pressure  by  a  small  pump,  or  else  the  oil  moves 
by  displacement,  as  in  the  Kamsbottom  lubricator  just  described. 
Small  copper  pipes  lead  the  oil  to  the  places  where  it  is  wanted. 
An  exception  is  supplied  by  big  ends  and  crank  pins,  which  are 
always  lubricated  by  hand.  They  are  fitted  with  large  oil  boxes. 
The  wick  is,  however,  no  longer  a  syphon,  but  a  plug  of  worsted 
loosely  coiled  into  a  double  copper  wire  and  pushed  into  the  pipe. 
In  these  rapidly  moving  parts,  the  oil  would  be  jerked  down  the 
pipe,  and  the  box  emptied  in  a  few  minutes,  if  it  were  not 
checked  by  the  worsted  plug. 


CHAPTEE   XXXIX 

BRAKES 

ALL  locomotives  in  the  present  day  are  fitted  with  automatic 
brakes.  These  are  rather  complex  systems  of  mechanism, 
and  nothing  more  can  he  given  here  than  a  general  description 
of  them. 

Up  to  about  the  year  1875  almost  nothing  had  been  done 
to  improve  on  the  very  elementary  screw  brake  on  the  tender 
and  in  the  guards'  vans,  by  which  segments  of  wood  were 
pressed  against  the  tires  to  stop  the  train.  These  were  very  in- 
efficient, and  involved  the  expenditure  of  much  labour  on  the  part 
of  the  fireman  and  the  guards.  Besides  the  risk  involved  there 
was  the  serious  delay  incurred.  Steam  had  to  be  shut  off  a 
couple  of  miles  outside  a  station,  and  the  train  brought  gradually 
to  rest.  Traffic  involving  frequent  stops  could  not  be  conducted 
rapidly,  because  a  train  had  scarcely  got  up  speed  before  steam 
had  to  be  shut  oft0  and  the  brakes  applied.  Many  inventors 
attempted  to  produce  something  better  than  the  screw  brake, 
but  the  only  successful  attempt  was  that  of  Messrs.  Newall  and 
Fay.  They  put  under  the  carriages  a  long  shaft  fitted  with 
screws,  which  applied  brake  blocks  to  the  wheels,  and  they 
coupled  these  rods  end  to  end  between  the  vehicles  by  a  very 
simple  universal  joint.  The  effect  was  that  the  guard,  instead 
of  braking  four  wheels,  only  could  brake  a  dozen.  The  invention 
was  used  with  some  success  on  the  Midland  Kailway  for  several 
years. 

To  George  Westinghouse,  a  young  American  engineer,  is  due 
the  credit  of  first  getting  the  Board  of  Trade  and  the  Eailway 
Companies  to  interest  themselves  in  brakes.  In  1875  a  good 
deal  of  money  was  spent,  and  "a  most  important  trial  of  various 


286  THE  EAILWAY  LOCOMOTIVE 

systems  took  place  at  Newark,  under  the  presidency  of  the  Duke 
of  Buckingham.  From  this  trial  may  be  dated  the  ultimate 
adoption  of  the  two  systems  in  use  to-day.  The  first  is  the 
pressure  system,  invented  by  Mr.  Westinghouse,  the  second  is 
the  vacuum  system,  invented  by  Mr.  Smith.  The  general 
principle  is  the  same  in  both.  A  pipe  extends  from  one  end  of 
the  train  to  the  other.  Under  the  coaches  this  pipe  is  of  iron, 
between  them  it  is  of  india-rubber ;  each  coach  has  its  own  length 
of  hose,  and  these  are  coupled,  when  the  train  is  made  up,  by  a 
highly  ingenious  joint. 

Under  each  coach  are  placed  cylinders  and  pistons,  the  rods  of 
which  work  cast  iron  brake  blocks  fitted  to  all  the  wheels. 

Taking  the  Westinghouse  brake  first,  the  brakes  are 
normally  kept  away  from  the  wheels  by  springs.  Under  each 
coach  is  a  small  reservoir  of  air  compressed  by  a  pump  on  the 
engine,  in  a  large  drum,  to  a  pressure  of  about  100  Ibs.  So  long 
as  there  is  an  equal  pressure  in  the  train  pipe  and  the  reservoirs 
the  brakes  remain  off.  But  each  cylinder  is  fitted  with  what  is 
known  as  the  "  triple  valve."  If  now  the  pressure  in  the  train 
pipe  is  reduced,  by  allowing  air  to  escape  from  it,  the  triple  valve 
moves  at  once  and  admits  air  from  the  small  reservoirs  to  the 
brake  cylinders.  The  pressure  instantly  applies  the  brake.  If 
the  train  were  to  part  in  two,  or  an  accident  happened,  the  hose 
joint  between  the  coaches  would  give  way,  the  air  would  run  out  of 
the  train  pipe,  and  the  brakes  would  be  applied  automatically. 
In  regular  work  the  driver  is  provided  with  a  valve  on  the  foot- 
plate by  opening  which  he  can  permit  the  air  to  escape  gradually 
from  the  train  pipe.  The  triple  valve  will  then  move  very 
slowly,  and  the  pressure  with  which  the  brakes  are  applied  can 
be  regulated  with  minute  accuracy.  To  take  the  brakes  off,  the 
train  pipe  is  replenished  from  the  main  reservoir,  which  is  in 
turn  filled  up  again  by  the  pump. 

The  vacuum  brake  is  in  all  but  details  identical.  Only  the 
air  in  the  train  pipe  and  reservoirs  is  exhausted  by  an 
ejector  on  the  engine,  which  works  on  the  same  principle  as  the 
blast  pipe.1  A  vacuum  is  maintained  on  both  sides  of  a  piston, 

1  See  page  151. 


BEAKES  287 

the  rod  of  which  is  connected  with  the  brakes.  If  now  air  is 
admitted  to  the  train  pipe,  a  valve  moves  and  air  gets  into  the 
cylinder,  and  pressing  with  a  force  of  15  Ibs.  on  the  square  inch 
at  one  side,  while  it  is  only  resisted  by  a  comparatively  small 
pressure  at  the  other  side,  the  brakes  are  put  on.  The  action 
is  controlled  from  the  footplate  by  a  valve  as  already  described. 
Both  systems  have  been  made  the  subject  of  many  patents. 

In  some  cases  the  vacuum  is  maintained  by  a  pump  worked  off 
a  cross  head  or  some  other  part  of  the  engine.  It  has  been  found 
impossible  to  prevent  leakage  altogether  ;  at  first  all  engines 
were  provided  with  a  large  and  a  small  ejector.  The  large  one 
established  the  vacuum,  and  the  small  one  maintained  it.  After 
a  time,  however,  it  was  found  that  the  small  ejector  wasted  much 
steam,  and  the  pump  was  substituted  with  quite  satisfactory 
results. 


CHAPTER  XL 

THE    RUNNING    SHED 

UNDER  this  comprehensive  title  will  be  considered  what  may 
without  inexactitude  be  termed  the  hidden  life  of  the  locomotive 
engine.  It  is  not  always  drawing  trains,  it  is  not  always  being 
repaired  or  repainted.  As  a  horse  spends  much  of  his  time  in 
the  stable,  so  does  the  locomotive  in  the  running  shed,  which 
has,  indeed,  not  inaptly,  been  termed  a  stable  ere  now. 

Originally  there  was  provided  a  shed,  literally  a  shed  and 
nothing  more,  in  which  the  engines  stood  when  not  at  work,  and 
in  which  they  were  cleaned  and  had  small  repairs  effected.  For 
many  years  and  in  the  present  day,  a  running  shed  is  a  large 
and  important  building,  often  provided  with  tools,  and  in  which  all 
but  very  heavy  repairs  can  be  effected.  Turntables  are  arranged 
and  many  lines  of  rail  with  pits  between  to  enable  men  to  work 
conveniently  under  the  locomotives. 

There  are  various  methods  of  laying  out  a  running  shed,  which, 
by  the  way,  is  called  a  "round  house"  in  the  United  States. 
Thus  the  general  plan  may  be  circular  with  a  turntable  in  the 
middle,  from  which  radiate  lines  of  rail  like  the  spokes  of  a  wheel. 
When  an  engine  comes  in  it  is  run  on  to  the  turntable,  which  is 
rotated  until  its  rails  coincide  with  a  "  spoke  "  on  which  there  is 
room.  The  engine  is  then  run  off  the  turntable  on  to  the  spoke. 
The  arrangement  is  very  convenient,  but  has  the  serious  draw- 
back that  if  anything  fouls  the  turntable  all  the  locomotives  in 
the  shed  are  imprisoned  for  the  time  being — an  accident  by  no 
means  unknown,  and  commonly  brought  about  by  moving  an 
engine  when  the  rails  on  the  table  are  not  in  line  with  those  of 
the  spoke.  Then  the  leading  wheels  of  the  engine  drop  into  the 
turntable  pit.  A  much  safer  system  consists  in  providing  a 


THE  KUNNING  SHED  289 

number  of  bays  and  shunting  an  engine  into  any  bay  by  means 
of  points.  More  space  is  required,  but  the  gain  fully  compensates 
for  the  extra  cost  incurred. 

The  running  sheds  are  placed  in  localities  as  convenient  as 
can  be  got  near  large  towns.  They  vary  in  the  amount  of 
accommodation  they  supply  from  holding  half  a  dozen  to  a 
hundred  engines. 

On  the  care  and  skill  with  which  the  duties  of  the  running- 
shed  foremen  and  the  hands  under  them  are  carried  out  depends 
in  very  large  measure  the  satisfactory  and  economical  working 
of  the  traffic  of  a  railway.  To  mention  only  one  point,  the 
durability  of  a  boiler  is  settled  in  the  main  by  the  way  in 
which  it  is  cleaned.  If  that  is  badly  done,  the  boiler  will  steam 
badly,  use  more  coal  than  it  ought,  and  fail  to  keep  time. 

Let  us  take  the  case  of  an  express  engine,  which  has  finished 
its  work  for  the  day.  It  is  unhooked  from  its  train,  and  taken 
to  the  running  shed.  The  duty  of  the  driver  before  handing 
it  over  to  the  "  engine  turner,"  a  man  whose  position  resembles 
that  of  an  ostler,  is  to  examine  the  engine  carefully  and  book  all 
the  defects  he  discovers.  The  turner  then  moves  the  engine  to 
the  coaling  stage,  the  fireman  locks  up  his  tool  chest  and  chalks 
on  one  of  the  boxes  how  much  coal  he  requires  for  his  next  trip. 
The  engine  is,  save  under  most  exceptional  circumstances,  to  be 
brought  to  the  end  of  its  journey  with  little  or  no  fire  on  the 
grate.  After  the  tender  has  received  the  stated  number  of  tons 
of  coal,  the  engine  is  moved  to  another  part  of  the  yard,  and  the 
smoke-box  is  cleaned  out.  As  has  already  been  explained,  the 
box  is  floored  with  fire-bricks  laid  in  fire-clay,  and  on  this  will  be 
found  collected  ash  and  cinders  which  have  been  carried  through 
the  flues.  A  spray  from  a  hydrant  is  used  to  keep  down  dust,  and 
the  box  is  cleared  out  by  a  lad  with  a  shovel  and  broom.  The 
engine,  which  has  still  steam  in  it,  is  then  moved  once  more  to 
stand  over  a  pit,  where  two  "  fire  droppers,"  one  on  the  footplate 
and  the  other  under  the  engine,  take  charge.  Then  some  fire 
bars  are  lifted  out,  and  through  the  space  thus  left,  ash,  cinders 
and  clinkers  are  dropped  into  the  ash  pan  by  the  man  on  the 
footplate,  while  his  mate  below  rakes  them  out  into  the  pit  where 

K.L.  u 


290  THE   RAILWAY  LOCOMOTIVE 

they  are  sprayed  by  a  hose  pipe.  In  this  operation,  simple  as  it 
seems  to  be,  we  have  another  illustration  of  the  importance  of 
doing  things  in  the  right  way.  It  seems  quite  obvious  that  it 
would  be  far  better  to  make  the  grate  invariably — as  is  done 
sometimes — with  a  hinged  portion  at  the  front  end  to  which  the 
bars  always  slope,  rather  than  adopt  the  clumsy  system  of 
pulling  two  or  three  or  more  bars  out.  But  the  drop  grate 
system  has  the  great  defect  that  if  it  is  used  while  the  boiler  is 
still  hot,  and  a  rush  of  cold  air  into  the  fire-box  takes  place, 
contraction  occurs  and  the  tubes  leak.  Indeed,  in  some  running 
sheds,  fire  dropping  is  not  permitted  while  a  boiler  is  hot,  and 
the  grate  has  to  be  cleaned  through  the  fire  door ;  but  the 
operation  lasts  about  half  an  hour,  and,  the  time  is  not  always 
available.  The  tubes  are  then  "  run  " — that  is,  swept  out.  A 
long  rod  about  f  inch  diameter  with  an  eye  at  the  end  is  used. 
Through  the  eye  is  threaded  a  strip  of  canvas  or  old  "  waste." 
The  smoke-box  door  is  opened  and  a  man  standing  on  the  front 
running  board  pushes  the  rod  through  one  tube  after  another. 
In  this  way  the  tubes  are  swept.  The  operation  lasts  from  forty 
minutes  to  an  hour,  according  to  the  number  of  tubes.  A  steam 
jet  at  the  end  of  a  hose  has  been  tried  with  great  success,  much 
time  being  saved. 

The  cleaners  then  take  the  engine  in  hand.  It  is  rubbed 
down  with  sponge  cloths  and  "  cleaning  oil,"  that  is,  petroleum. 
The  cleaners  are  boys  or  lads.  Cleaning  is  the  first  step  on  the 
way  to  be  an  engine  driver. 

Round  the  ends  of  the  tubes  next  the  fire-box  rings  of  coke 
deposit  (due  to  the  presence  of  minute  percentages  of  iron  in  the 
coal)  form  and  encroach  on  the  size  of  the  orifice.  A  boy  goes 
into  the  fire-box  with  a  stiff  broom  and  knocks  off  the  "  corks,"  as 
they  are  called — they  are  termed  "  birds'  nests  "  at  sea  ;  they  very 
closely  resemble  india-rubber  umbrella  rings.  He  then  sweeps  the 
ashes  off  the  top  of  the  brick  arch,  and  replaces  the  fire-bars.  The 
engine  is  then  ready  to  have  steam  got  up  again.  The  "  lighter-up" 
puts  coal  into  the  box,  spreading  it  carefully  all  round  the  sides. 

Conveniently  situated  is  a  brick  furnace  of  considerable  size. 
On  the  top  of  this  sand  is  dried  which  is  subsequently  put  into 


THE  EUNNING   SHED  291 

the  sand  boxes  on  the  engine  and  used  for  increasing  adhesion,  as 
already  explained.  On  the  Great  Western  Kailway  an  improved 
furnace  is  used.  The  wet  sand  is  put  into  a  chamber  with  a 
grated  bottom  over  the  horizontal  flue  leading  to  the  chimney, 
and  as  the  sand  dries  it  falls  automatically  through  the  hot  gas 
and  flame.  About  five  times  as  much  sand  can  be  dried  in  a 
given  time  in  this  way  as  by  the  ordinary  furnace. 

From  this  furnace  some  shovelfuls  of  burning  coal  are  carried 
and  put  into  the  fire-box,  and  so  lighting  up  is  effected.  As  the 
fires  are  not  to  be  hurried,  which  would  be  bad  for  the  boilers, 
it  requires  about  three  hours  to  get  up  steam ;  and  the  fire  is 
usually  lighted  about  four  hours  before  the  time  at  which  the 
train  starts.  While  in  the  shed  the  fireman  takes  in  water  and 
fills  the  sand  boxes.  The  driver  goes  over  the  whole  engine  with 
minute  care,  examining  every  split  pin,  nut  and  bolt,  knowing, 
as  he  does,  that  his  own  life  and  the  safety  of  the  train  depend 
upon  his  vigilance. 

It  has  been  assumed  that  the  engine  requires  neither  washing 
out  nor  repairs.  But  washing  out  must  take  place  every  five  or 
six  days.  To  this  end,  the  engine  is  allowed  to  cool  down,  then 
the  plugs  at  the  lower  corners  of  the  fire-box  are  unscrewed,  and 
the  water  is  allowed  to  run  out.  All  the  other  wash-out  plugs 
are  removed,  and  the  boiler  is  then  cleaned  out  by  the  use  of 
a  jet,  by  preference  of  hot  water,  the  nozzle  being  put  into  one 
plug  hole  after  another.  While  one  man  uses  the  hose,  another 
works  with  a  rod  to  scoop  out  and  loosen  all  the  deposit  he  can  get 
at.  The  boiler  is  then  examined,  preferably  by  a  boilermaker. 
If  he  pronounces  it  clean  the  plugs  are  oiled  with  some  heavy 
oil  and  screwed  in  again.  The  boiler  is  filled  up  with  fresh  water 
by  a  hose  through  one  of  the  upper  plug  holes.  Washing  out  is 
a  very  important  operation.  A  book  is  kept  in  which  are 
entered  under  separate  heads,  date,  station,  number  of  engine, 
name  of  washer,  by  whom  examined,  and  remarks  as  to  dirt. 
When  tubes  leak,  neglect  in  washing  out  is  always  assumed  as  a 
probable  cause. 

While  in  the  running  sheds  that  careful  inspection  takes  place 
which  renders  the  explosion  of  a  locomotive  boiler  an  event  of 

u2 


292  THE  EAILWAY  LOCOMOTIVE 

the  rarest  occurrence.  Practice  varies,  but  it  is  not  far  from  the 
truth  to  say  that  more  than  a  month  seldom  elapses  without  an 
examination  of  a  very  thorough  character  being  made  by  a  boiler- 
smith.  As  a  rule  there  is  little  trouble  with  the  shells ;  grooving 
and  corrosion  are  rare,  and  are  detected  when  the  lagging  is 
taken  off  and  tubes  drawn  for  a  thorough  repair,  which  will  not 
be  needed  as  a  rule  for  three  or  four  years.  But  the  fire-box  is 
a  continual  source  of  anxiety.  The  wear  and  tear  have  been 
much  increased  by  the  rise  in  pressure.  Boxes  which  give  little 
or  no  trouble  with  150  Ibs.  steam  require  the  utmost  vigilance 
to  make  them  endure  200  or  220  Ibs.  pressure.  The  higher  the 
pressure  the  denser  becomes  the  deposit  and  the  more  firmly 
does  it  cling  to  the  plates.  A  fairly  soft  water  is  essential  to 
the  well-being  of  the  modern  locomotive.  The  most  common 
defects  in  a  copper  internal  fire-box  are  cracks.  The  examiner 
has  a  special  book  in  which  he  records  in  a  species  of  shorthand 
all  the  defects  which  he  finds.  A  great  deal  of  information  is 
got  into  a  small  space  by  a  system  of  hieroglyphics.  As  an 
example  of  the  progress  of  events  in  the  life  of  a  locomotive 
boiler,  the  following  statement  is  given  :— 

"  Nothing  of  note  occurred  to  the  box  during  that  year,  but  on 
January  13,  1904,  the  stay  heads  were  slightly  reduced.  Fifteen 
new  stays  were  put  in  on  January  27,  1904.  The  stays  were 
reported  reduced  on  April  19,  and  on  May  12  a  crack  had 
developed  in  the  right-hand  flange  of  the  tube  plate ;  also,  the 
top  flange  of  the  back  plate  had  dropped  down  near  the  second 
crown  bars.  On  August  23  the  tubes  were  dirty,  and  the 
casing  plates  were  corroded  near  the  foundation  ring.  On 
August  30,  1904,  eighty-four  new  tubes  were  put  in  to  replace 
those  taken  out  to  facilitate  the  removal  of  dirt,  and  this  time 
also  the  sides  were  found  to  be  slightly  bulged.  Twelve  more 
stays  were  put  in  on  April  11,  1905,  and  on  September  12 
another  crack  had  developed  in  the  tube  plate,  this  time  in  the 
left-hand  flange,  and  the  sides  which  had  been  previously  reported 
as  "slightly  bulged  "  were  reported  as  "bulged."  On  October  17, 
the  tubes  were  again  reported  dirty,  and  after  the  engine  had 
been  kept  running  as  long  as  it  consistently  could  be  in  this 


THE  ETJNNING   SHED  293 

condition,  it  was  sent  to  the  factory  for  general  repairs  on 
January  31,  1906." 

The  preceding  quotation  is  taken  from  a  paper  read  before 
the  Swindon  Engineering  Society  by  Mr.  Henry  Simpson,  of  the 
Great  Western  Eailway. 

It  must,  of  course,  be  understood  that  running-shed  work  is 
not  carried  on  in  the  same  way  on  all  railways.  No  more  can  be 
done  than  give  the  general  arrangements  and  methods  adopted. 
Thus,  for  example,  on  some  lines  it  is  the  practice  to  coal  the 
engines  after  they  have  been  cleaned  and  left  the  running  shed, 
but  in  effect  practice  is  the  same  everywhere. 

A  locomotive  is  not  cleaned  after  every  trip  as  described  above. 
Slag  is  taken  off  the  grate  by  the  fireman,  and  the  tabes  are  run 
and  the  smoke-box  cleaned  out,  but  steam  is  not  let  down  below 
80  or  100  Ibs.  pressure,  and  a  fresh  supply  of  coal  is,  if  needed, 
put  on  the  tender. 

The  day's  work  of  an  engine  is  very  often  worked  out  as  though 
it  had  been  running  steadily  from  the  time  steam  was  got  up 
until  it  returned  to  the  shed.  The  mileage  varies  with  the 
railway,  the  time  of  the  year,  and  traffic  conditions.  At  one 
time  on  the  London  and  Brighton  line  it  was  four  miles  an  hour 
for  goods  and  about  eight  miles  an  hour  for  passenger  engines. 
A  goods  engine,  for  example,  will  be  under  steam  and  out  on  the 
road  for  say,  fourteen  hours.  Of  that  time,  five  hours  will  be 
spent  standing  still.  Two  or  three  hours  will  be  used  up  at 
different  stations  shunting,  the  whole  distance  traversed  being 
quite  small.  The  rest  of  the  time  the  engine  will  spend  in 
hauling  heavy  trains  at,  say,  twenty  miles  an  hour. 

The  average  annual  mileage  of  engines  in  this  country  is  about 
20,000.  Of  course  to  this  there  are  numerous  exceptions,  the 
mileage  being  much  greater.  Individual  engines  sometimes 
make  enormous  mileages.  In  the  United  States  it  is  very  much 
higher,  but  as  a  result  the  total  life  of  the  engine  and  the  number 
of  miles  run  is  less.  The  American  locomotive  is  treated  very 
much  on  the  principle  followed  by  Legree  with  his  slaves,  "  use 
up  and  buy  more." 


CHAPTEK  XLI 

THE    WORK    OF    THE    LOCOMOTIVE 

WE  have  now  to  consider  the  work  of  a  locomotive — the  duty 
which  a  machine  so  ingenious,  so  complex,  and  so  carefully  and 
cautiously  developed  has  to  perform. 

In  one  sense  this  admits  of  being  very  easily  stated.  The 
business  in  life  of  the  locomotive  is  to  pull.  Its  value  from  the 
railway  companies'  point  of  view  is  estimated  in  terms  of  this 
central  fact — a  fact  which  must  be  carefully  kept  in  mind.  All 
the  various  devices  for  securing  power  and  economy  have,  after 
all,  no  other  ultimate  object  than  the  securing,  other  things 
being  equal,  of  the  greatest  possible  tractive  effort  for  the  smallest 
outlay  of  money.  At  first  sight  it  might  appear  that  speed  is  an 
important  element  in  our  calculations.  It  will,  however,  be  seen 
presently  that  speed  itself  depends  on  tractive  effort.  Once  more, 
other  things  being  equal,  the  engine  which  can  pull  hardest  will 
run  fastest.  Now  the  drawbar  pull  will  always  be  precisely 
equal  to  the  reaction  of  the  wheels  at  the  points  where  they  rest 
on  the  rails,  less  the  amount  required  to  overcome  the  rolling  or 
road  resistance  of  the  engine  and  tender.  Deducting  this  last 
we  have  the  net  pull  on  the  hook  at  the  back  of  the  tender  left 
for  drawing  the  train. 

The  precise  way  in  which  the  engine  is  propelled  has  already 
been  fully  explained  on  page  66,  but  this  has  nothing  whatever 
to  do  with  the  action  of  the  wheel  on  the  rail  as  a  fulcrum.  The 
wheel  continually  tries  to  push  the  rail  backwards,  and  failing  in 
this  it  rolls  forward,  and  with  it  the  engine  and  train.  We  have 
then,  before  we  can  arrive  at  any  just  estimate  of  the  hauling 
power  of  a  locomotive,  to  ascertain  what  this  power  may  be.  It 
is  always  calculated  by  a  formula  for  which  the  world  is  indebted 


THE  WOEK  OF  THE  LOCOMOTIVE  295 

to  the  Chevalier  F.  M.  G.  De  Pambour,  a  young  French 
engineer,  who  carried  out  a  remarkable  series  of  experiments  on 
the  Liverpool  and  Manchester  Kailway.  The  results  took  the 
form  of  a  treatise  published  first  in  France  in  1835.  Sub- 
sequently an  excellent  translation  was  published  in  English,  in 
Philadelphia  in  1836. 

The  formula  is  very  simple  :  — 

Let  D  be  the  diameter  of  the  driving  wheel  in  inches. 

,,    d       „      diameter  of  the  cylinder  in  inches. 

,,   L       „      length  of  stroke. 

„  P       „      average    effective    pressure    in   the   cylinder   in 
pounds  per  square  inch. 

Then  d*  X  ^  x    P  =  T,  the  tractive  effort. 

Only  one  cylinder  is  to  be  taken  ;  usually  P  is  taken  as  unity. 
The  result  of  the  calculation  is  the  tractive  effort  with  a  cylinder 
pressure  of  one  pound,  which  can  be  regarded  as  the  coefficient 
for  the  engine.  Thus,  let  T  =  tractive  power. 

D  =  60  ;    d  =  20. 

L  =  24  and  P  =  1. 


Then  T  =  =  160  Ibs.     This  is  the  tractive  effort  at 

bU 

the  points  where   the  driving  wheels  touch  the  rails  for  every 
pound  of  average  effective  pressure    in    the    cylinders.     It    is 
divided  up  among  the  wheels  ;  if  there  are  two  driving  wheels, 
then  it  is  80  Ibs.  each  ;  if  four,  40  Ibs.  each,  and  so  on. 
For  compound  locomotives,  the  formula  becomes 

1-6  P  r"  L 

'  D  (2  +  1)' 

where  T  =  tractive  power,  d  =  diameter  of  low  pressure 
cylinder,  L  =  length  of  stroke,  r  the  ratio  of  the  cylinder  volumes, 
and  D  =  the  diameter  of  the  driving  wheels.  Normally,  a  deduc- 
tion of  20  per  cent,  is  made  in  all  cases  to  cover  the  resistance 
of  the  engine  and  tender,  that  is  to  say,  the  rolling  or  road 
resistance. 

As  the  formula  puzzles  the  student  in  some  cases,  because 
only  one  cylinder  is  taken  although  there  are  two,  the  following 


296  THE  RAILWAY  LOCOMOTIVE 

passage  is  reproduced  from  Pambour's  book,  which  explains  how 
he  obtained  it. 

"  If  we  find  that  the  steam  by  causing  a  known  effective 
pressure  per  square  inch  can  make  the  engine  advance,  the  area 
of  the  two  pistons  in  square  inches  being  known,  it  is  easy  to 
calculate  the  total  force  applied  by  the  steam  on  those  two 
pistons.  That  force  being  sufficient  to  make  the  engine  advance 
— that  is  to  say,  to  conquer  its  resistance — it  gives,  of  course, 
the  value  of  that  resistance.1  It  must  only  be  observed  according 
to  the  principle  known  in  Mechanics  by  the  name  of  "  The 
Principle  of  Virtual  Velocities,"  that  the  pressure  exercised  on 
the  part  of  an  engine  being  transmitted  to  another  part  of  the 
same  engine  retains  the  same  intensity  only  in  case  the  two 
parts  have  the  same  velocity.  If  not,  the  force  of  pressure  is 
reduced  in  an  inverse  ratio  to  the  velocity  of  the  points  of 
application.  This  principle  appears  in  an  evident  manner,  and 
a  priori  in  simple  machines  like  the  lever,  the  roll,  the  pulley, 
and  an  inspection  alone  is  sufficient  to  demonstrate  that,  if  a 
force  can  by  the  aid  of  the  machine  raise  a  weight  four  times 
as  great  as  itself,  it  is  only  by  travelling  in  the  same  space  of 
time  four  times  as  far  as  the  weight  which  it  raises.  In  the  case 
before  us  the  velocity  of  the  piston  is  to  that  of  the  engine  as 
twice  the  stroke  is  to  the  circumference  of  the  wheel,  the  piston 
giving  two  strokes  while  the  wheel  turns  once  round.  A  force 
applied  on  the  piston  produces  therefore  in  regard  to  the  progress 
of  the  engine  an  effect  reduced  in  the  same  proportion,  that  is  to 
say,  as  twice  the  stroke  is  to  the  circumference  of  the  wheel. 

"  Let  d  be  the  diameter  of  the  piston,  and  -n  the  ratio  of  the 
circumference  to  the  diameter,  \  TT  d2  will  be  the  area  of  one  of 
the  two  pistons,  and  P  being  the  effectual  pressure  of  the  steam  per 
square  inch,  then  J  TT  rf2  P  will  be  the  effective  pressure  upon  the 
two  pistons.  If,  moreover,  I  expresses  the  length  of  the  stroke, 

1  It  is  worth  notice  that  this  appears  to  be  the  first  recognition  of  the 
fact  that  there  is  no  such  thing  as  an  unbalanced  force.  Previously,  and  for 
many  years  subsequently,  it  was  always  taken  for  granted  that  unless  a 
force  exceeded  the  resistance  there  could  be  no  motion ;  that  the  resistance 
of  a  train  was  always  less  than  the  pull  of  the  engine,  the  resistance  to  a 
piston  less  than  the  pressure  on  it. 


THE  WORK  OF  THE  LOCOMOTIVE  297 

and  D  the  diameter  of  the  wheel,  the  effective  force  of  transfer 
resulting  to  the  engine  in  consequence  of  that  transfer  will  be 


which,  according  to  what  we  have  said,  gives  the  measure  of  the 
resistance  of  the  engine." 

It  must  be  understood  that  the  word  "  resistance  "  refers  here 
to  the  rolling  and  not  to  the  frictional  resistance  of  the  locomotive. 
In  other  words,  the  equation  gives  the  tractive  effort. 

A  little  thought  will  suffice  to  show  that  there  must  be  some 
definite  speed  which,  multiplied  by  the  drawbar  pull,  will  give 
maximum  efficiency.  The  pull  steadily  falls  off  as  the  speed 
increases,  because  the  average  effective  pressure  diminishes, 
partly  because  of  wire  drawing  and  partly  because  the  boiler 
cannot  make  enough  steam.  What  this  speed  will  be  depends 
on  various  conditions.  It  is  known  as  the  critical  speed,  and  is 
in  all  cases  comparatively  low.  It  is  impossible  to  go  fully  into 
the  question  here.  But  something  must  be  said  in  the  way  of 
explanation.  Professor  Goss's  investigations  go  to  show  that  it 
is  always  about  200  revolutions  per  minute,  no  matter  what  the 
size  of  the  driving  wheel  (vide  page  301)  . 

The  question  of  train  resistance  has  been  made  the  subject  of 
most  elaborate  and  costly  investigation,  and  even  yet  it  cannot 
be  said  that  conclusive  results  have  been  obtained.  Nothing 
more  can  be  done  here  than  give  three  formulae.  The  first  has 
been  obtained  by  Mr.  Deeley,  on  the  Midland  Railway  : 

V2  « 

B  =  3-25  +  jg 

The  second  is  by  M.  Laboriette,  a  French  engineer  : 


These  do  not  apply  to  speeds  below  twenty  miles  an  hour,  when 
the  resistance  of  the  axle  is  higher  than  at  quick  speeds.  The 
following  formula  of  general  application  to  all  speeds  has  been 
prepared  by  Mr.  Wolff: 


+  3  /    '    300' 


298  THE  EAILWAY  LOCOMOTIVE 

Owing  to  the  great  weight  and  enormous  momentum  of  a 
locomotive,  it  might  be  supposed  that  its  drawbar  pull  would  be 
perfectly  steady,  but  it  is  not.  It  will  be  remembered  that  not 
all  the  reciprocating  motion  can  be  counterpoised,  and  there  are 
besides  the  internal  disturbing  forces  due  to  the  varying  crank 
moments  and  piston  pressures.  On  the  testing  plant  at  the 
St.  Louis  Exhibition,  to  which  reference  has  already  been  made, 
the  locomotives  pulled  on  a  tractometer,  which,  being  fitted  with 
a  recording  pencil,  gave  a  diagram  of  the  pull. 

Three  tractometer  diagrams  have  been  selected  from  a  con- 
siderable number,  and  are  here  given;  they  are  from  "  Locomotive 


6000  -i 


4000  -  ^ 
MAAA/UVWU\A/\AA/WVA^ 

nrauhnr    Pull-/  ' 


4000  - 
AAAAAAAAAAAAAA/U 

*"'   '  zooo  H 

Datum  L/ne-^ 


rest  J/J 

Dasfijxte  m  Safety-Bars   Throttled 

Speed,  66.06  Miles  per  Hour. 
FlG.  91. 

Tests  and  Exhibits."  Fig.  91  is  from  a  De  Glehn  compound 
four-cylinder  engine  very  similar  in  all  respects  to  La  France, 
which  attracted  much  attention  when  first  put  to  work  some 
three  years  ago  on  the  Great  Western  Kailway.  The  amount  of 
the  pull  in  pounds  is  shown  at  the  right-hand  end  of  the  diagram, 
which  it  will  be  understood  is  a  portion  of  a  continuous  trace  made 
on  a  strip  of  paper  moving  under  a  pencil.  The  form  of  the 
trace  is  somewhat  modified  by  the  action  of  two  dash  pots 
placed  at  the  anchorage.  The  levelling  effect  of  four  cylinders 
is  manifested.  The  difference  in  pulls  does  not  much  exceed 
about  300  Ibs. 

The  diagram,  Fig.  92,  is  one  from  a  very  heavy  "  simple  "  freight 
engine,  with  eight  wheels  coupled  53  inch  diameter,  two  cylinders 
21  inches  X  30  inches.  It  will  be  seen  that  at  fifteen  miles  an 


THE  WORK  OF  THE  LOCOMOT1YE  299 

hour  the  maxim  pull  reached  about  22,000  Ibs.,  the  difference 
in  pulls  being  as  much  as  1,500  Ibs.     The  third  diagram  is  from 


26000 -\ 


MJ^ 


Drvvbar  Pu//- 

/5000- 

/oooo- 

5000- 

Datum 


No  Dasfipote  //?  Safety 

Speed*  14.99  Miles  per  Hou 

FIG.  92. 


the  same  engine  at  a  little  under  thirty  miles  an  hour  ;  the 
average  pull  has  fallen  to  10,000  Ibs.,  but  the  difference  between 
the  highest  and  the  lowest  is  now  about  2,100  Ibs.  The  causes 


/woo- 


'MMM/WMMMWMIJWMMMM^ 

Dramas  PultJ  4  ^ 


Datum 


n  3afety  Bars 

Sfeed>  29.87  Mila  per  Hour. 

FIG.  93. 

of  the  vibration  have  already  been  explained.  It  will  be  under- 
stood that  each  "  saw  tooth  "  stands  for  one  complete  revolution 
of  the  driving  wheels.  The  total  motion  of  the  draw  bar  did  not 
exceed  0'04  inch,  so  that  a  locomotive  exerting  a  drawbar  pull 


300  THE  BAIL  WAY  LOCOMOTIVE 

equal  to  the  full  capacity  of  the  dynamometer1  did  not  move 
forward  on  the  supporting  wheels  more  than  this  amount.  The 
motion  was  increased  200  times  at  the  recording  pen,  or  for  each 
one  hundredth  of  an  inch  that  the  locomotive  moved  forward 
the  recording  pen  moved  through  a  space  of  two  inches,  the 
total  movement  being  8  inches  for  the  0*04  inch  movement. 

It  might  be  supposed  that  when  the  engine  is  drawing  a  train 
its  own  momentum  would  extinguish  the  vibration,  but  in  point 
of  fact  it  does  not,  and  the  trace  taken  in  a  tractometer  van  is 
very  similar  in  character  to  that  obtained  in  the  test  house. 

The  actual  performance  of  locomotives  is  very  varied.  A 
complete  record  of  all  that  has  been  noteworthy  in  this  country 
and  in  France  has  been  supplied  periodically  for  several  years 
past  to  the  Engineer  by  the  late  Mr.  Charles  Ecus  Marten,  which 
record  will  be  found  most  interesting  reading. 

Much  is  heard  now  and  then  about  trains  making  up  lost  time, 
and  drivers  are  censured  by  the  public  for  incurring  risks  ;  but 
as  a  matter  of  fact,  it  is  extremely  difficult,  particularly  with  fast 
trains,  to  make  up  lost  time.  Mr.  Ivatt  several  years  ago 
prepared  a  very  useful  diagram.  Fig.  94,  which  sets  this  truth  in 
a  very  clear  light. 

As  an  example,  if  a  train  running  at  sixty-five  miles  per  hour 
has  lost  a  minute,  it  has  to  run  fifteen  miles  at  seventy  miles 
per  hour  in  order  to  make  up  that  minute,  showing  prominently 
what  a  great  length  of  line  must  be  run  over  in  order  to  make 
up  even  so  small  an  amount  of  time  as  one  minute. 

The  diameters  of  the  driving  wheels  of  all  but  the  smallest 
locomotives,  such  as  those  used  by  contractors  and  in  engineering 
and  iron  works,  vary  between  4  feet  and  8  feet.  Goods  engines 
have  driving  wheels  as  a  rule  not  often  less  than  4  feet  6  inches 
or  more  than  5  feet  6  inches.  Passenger  engine  driving  wheels 
are  in  the  present  day  5  feet  6  inches  to  7  feet  9  inches  diameter. 
No  engines  are  now  being  made  with  8-feet  wheels,  but  a  few 
are  still  running.  Very  early  in  the  history  of  railways  it  came 
to  be  understood  that  large  diameters  and  speed  went  together, 

1  This  is  the  recognised  term,  but  as  it  may  cause  confusion  the  author 
prefers  to  use  the  word  "  tractometer,"  about  which  no  mistake  can  arise. 


THE  WOEK  OF  THE  LOCOMOTIVE 


301 


MINUTES  PE 


MILES  pea  HOUR 


53         60       63 


but  about  the  precise  reason  why  no  one  was  troubled.  Indeed, 
it  was  not  till  some  ten  years  ago,  when  Professor  Goss,  of 
Purdue  University,  U.S.A.,  undertook  his  investigations,  that 
the  facts  were  reduced  to  a  sound  numerical  basis. 

The  steaming  power  of  the  boiler  is  the  final  measure  of  that 
of  the  whole  machine.  It  may  be  taken  as  proved  that  a 
locomotive  boiler  may  be  depended  upon  to  evaporate  12  Ibs.  of 
water  per  square  foot  of  heating  surface  per  hour.  Thus  a 
boiler  with  1,300  square  feet 
will  make  15,600  Ibs.  of 
steam  per  hour. 

Now  the  dimensions  of 
cylinders  are  fixed  by  con- 
ditions which  have  been  fully 
explained  in  preceding  pages. 
It  will  be  seen  at  once  that 
whether  the  full  power  of 
the  boiler  is  or  is  not  to 
be  utilised  depends  on  how 
many  times  each  cylinder 
can  be  filled  and  emptied 
in  a  minute.  Suppose  that 
our  cylinders  are  too  small, 
then  let  us  run  the  engine 
faster.  But  the  speed  of  the 

train  is  fixed  by  traffic  managers.  Let  us  meet  this  objection 
by  reducing  the  diameter  of  the  driving  wheels.  But  this  will 
not  do  for  reasons  already  explained.  Wire  drawing  steps 
in,  the  consumption  of  steam  per  stroke  falls  off,  and  so  does 
the  mean  effective  cylinder  pressure.  If  the  horse  power  of  the 
boiler  is  a  constant,  then  T  S  will  also  be  a  constant.  Here  T 
is  the  tractive  effort  and  S  the  speed  in  miles  per  hour.  That 
is  to  say,  the  tractive  effort  will  fall  off  as  the  speed  augments, 
and  a  curve  plotted  for  various  speeds  and  tractive  efforts  is  a 
hyperbola.  The  tractive  effort  depends  on  the  mean  pressure 
in  the  cylinder,  and  that  may  be  so  much  reduced  by  wire 
drawing  that  an  engine  with  small  wheels  may  be  quite  unable 


FIG.  94. 


302  THE  EAILWAY  LOCOMOTIVE 

to  use  up  all  the  steam  the  boiler  can  make,  and  so  actually 
exert  less  pull  than  an  engine  with  larger  wheels.  If  the  reader 
will  follow  this  reasoning  out  he  will  find  that  for  normal  loco- 
motives about  200  revolutions  per  minute,  or  800  strokes  for  the 
two  cylinders,  may  be  regarded  as  the  limiting  condition  for 
the  exertion  of  maximum  drawbar  pull.  In  other  words,  T  S  then 
represents  the  maximum  power  which  the  engine  can  exert.  If  this 
is  so,  then  if  30  miles  an  hour  corresponds  with  200  revolutions 
per  minute,  60  miles  an  hour  will  demand  driving  wheels  of 
twice  the  diameter.  One  eminent  builder  of  locomotives  in  the 
United  States  holds  that  driving  wheels  should  have  one  inch 
diameter  for  every  mile  an  hour  of  maximum  speed.  But  this 
gives  a  5-feet  wheel  for  60  miles  an  hour,  which  is  much  too 
small. 

To  make  this  reasoning  clearer,  the  following  experiment  is 
quoted  from  Professor  Goss's  book  "Locomotive  Performance." 
"  A  particular  engine,  with  a  nominal  cut-off  at  35  per  cent,  of 
the  stroke,  when  making  188  revolutions  per  minute,  had  a 
mean  effective  cylinder  pressure  of  42*4  Ibs.  and  the  tractive 
effort  T  =  4,639  Ibs.  But  to  run  this  engine  at  55  miles  an 
hour  and  296  revolutions  per  minute  the  mean  pressure,  the 
nominal  cut-off  remaining  unaltered,  fell  to  27'4  Ibs.  and  the 
tractive  effort  to  2,997  Ibs.  The  wheels  were  5  feet  3  inches  in 
diameter.  If  they  had  been  increased  to  8  feet  3  inches  the 
speed  would  have  been  55  miles  an  hour,  the  revolutions  188, 
and  T  =  2,943  Ibs.,  the  loss  in  tractive  effort  due  to  this 
increase  in  the  size  of  the  driving  wheels  being  almost  entirely 
compensated  by  the  maintenance  of  a  high  mean  cylinder 
pressure." 

It  must  not  be  forgotten,  however,  that  the  engine  with  the 
big  drivers  would  start  very  badly  as  compared  with  that  with 
the  small  wheels. 

Enough  has  been  said  to  show  that  the  determination  of  the 
diameter  of  driving  wheels  to  give  the  best  results  is  a  very 
delicate  point.  The  facts  go  far  to  explain  why  it  is  that  small 
differences  in  the  diameters  of  driving  wheels  may  produce  results 
apparently  out  of  all  proportion  to  the  differences. 


THE    WORK  OF   THE  LOCOMOTIVE  303 

There  is  apparently  no  limit  to  what  might  be  said  about  the 
railway  locomotive.  The  book  to  which  these  words  form  the 
conclusion  deals  with  many  subjects,  each  and  every  one  of 
which  might  well  receive  fuller  treatment.  The  locomotive 
grows  with  the  growth  of  nations ;  it  has  been  a  principal  agent 
in  the  extension  of  civilisation.  To  it  is  due  the  modern  great 
city  and  the  spread  of  commerce.  No  other  machine  is  so 
ostensible  ;  it  is  always  before  the  public.  No  other  is  more 
flexible  or  ready  to  render  service  under  most  varying  condi- 
tions, probably  none  other  does  so  much  useful  work.  It  is  the 
only  machine  that  appears  to  be  alive.  It  is  almost  impossible 
indeed  to  watch  one  start  its  train  or  thunder  through  a  station 
and  escape  the  sensation  that  we  have  a  sentient  being  in 
evidence.  It  has  been  said  that  electricity  will  supersede  it. 
Possibly,  but  the  time  is  not  near.  Whenever  and  wherever,  the 
locomotive  engine  will  still  remain  immortal.  Its  history  may 
indeed  be  forgotten  or  overlooked  by  future  generations.  But 
among  those  who  admire  and  love  mechanism  and  the  mechanical 
arts  will  always  be  found  a  few  who  will  keep  its  memory  green, 
and  that  of  the  men  to  whose  genius,  talents,  and  indomitable 
energy  the  world  is  indebted  for  the  most  wonderful  machine 
ever  devised. 


STANDARD  WORKS  ON   THE  LOCO- 
MOTIVE ENGINE 


A  Practical  Treatise  on  Railroads  and  Internal  Communications  in  General. 
By  Nicholas  Wood.  London:  Longman.  1832. 

A  Practical  Treatise  on  Locomotive  Engines  upon  Railways.  By  the 
Chevalier  F.  M.  G.  De  Pambour.  Philadelphia:  Carey  &  Hart.  1836. 

The  Machinery  of  Railways.     By  D.  K.  Clark.     1855. 

On  Heat  and  its  relation  to  Water  and  Steam.  By  Charles  Wye  Williams. 
Longman.  1860. 

The  Internal  Disturbing  Forces  of  the  Locomotive.  By  J.  Makinson. 
Trans.  Inst.  C.  E.  1862. 

Locomotive  Engineering  and  the  Mechanism  of  Railways.  By  Zerah 
Colburn,  completed  by  W.  H.  Maw  and  D.  K  Clark.  Glasgow :  William 
Collins.  1864. 

Experimental  Researches  in  Steam  Engineering,  Vol.  II.  By  Benjamin 
Isherwood.  Philadelphia :  Franklin  Institute.  1865. 

Treatise  on  the  Locomotive  Engine.  By  G.  D.  Dempsey.  Weale's  Series. 
London  :  Crosby  Lockwood  &  Co.  1879. 

The  Construction  of  Locomotive  Engines.  By  W.  Stroudley.  Trans. 
Inst.  C.  E.  1885. 

Counterbalancing  Locomotives.  By  Edmund  Lewin  Hill.  Trans.  Inst. 
C.  E.  1891. 

The  Construction  of  the  Modern  Locomotive.  By  George  Hughes. 
London  :  E.  &  F.  N.  Spon.  1894. 

Valves  and  Valve  Gearing.  A  practical  text-book,  by  Charles  Hirst. 
London  :  Charles  Griffin  &  Co.  1897. 

The  Evolution  of  the  Locomotive  Engine.  By  W.  P.  Marshall.  Trans. 
Inst.  C.  E.  1898. 

The  Steam  Engine  Indicator.  By  Cecil  H.  Peabody.  New  York :  John 
Wiley  &  Sons.  1900. 

Locomotive  Operation.  A  Technical  and  Practical  Analysis.  By  G.  R. 
Henderson,  M.A.S.M.E.  Chicago:  The  fiaifwfn/  Aye.  1904. 

B.L.  X 


306  APPENDIX 

The  Pennsylvania  Railroad  System  at  the  Louisiana  Purchase  Exhibition. 
Locomotive  Tests  and  Exhibits,  St.  Louis,  Missouri,  1904.  Philadelphia: 
The  Pennsylvania  Eailroad  Co.  1905. 

La  Locomotive  Actuelle.  Etude  Generale  sur  les  Types  Recents  des  Loco- 
motives .a  Grande  Puissance.  Par  Maurice  Demoulin,  Ingenieur  de  la 
Traction,  Chemin  de  fer  de  1' Quest.  Paris  :  Beranger.  1906. 

Die  Dampflokomotiven  der  Gegenwart.  Ein  Handbuch  fur  Lokornotiv- 
bauer.  Eisenbahnbetriebsbearnte  und  Studierende  des  Maschinenbaufachs. 
Yon  Robert  Garbe,  Geheimen  Baurat,  Mitglied  der  Kgl.  Eisenbahndirektion, 
Berlin.  1907. 

Locomotive  Performance.  The  Result  of  a  Series  of  Researches  conducted 
by  the  Engineering  Laboratory,  Purdue  University,  U.S.A.  By  W.  F.  M. 
Goss,  M.S.  New  York:  JohnViley  &  Sons.  1907. 

Bulletin  of  the  International  Railway  Congress.  English  edition,  pub- 
lished monthly.  London  :  King  &  Sons. 

The  Locomotive  Catechism.  By  Robert  Grimshaw.  New  York:  Norman 
W.  Henley  &  Co.  London :  E.  &  F.  N.  Spon.  1893. 

Train  Resistance.     By  J.  A.  F.  Aspinall.     Trans.  Inst.  C.  E.     1901. 

History  of  the  Furness  Railway.  By  W.  F.  Pettigrew.  Trans.  Inst.  Mech. 
Eng.  1901. 

Recent  Locomotive  Practice  in  France.  By  Edouard  Sauvage.  Trans. 
Inst.  Mech.  Eng.  1900. 

Experiments  on  the  Draught  produced  in  different  parts  of  a  locomotive 
boiler  when  running.  By  J.  A.  F.  Aspinall.  Trans.  Inst.  Mech.  Eng.  1 893. 

Superheaters  applied  to  Locomotives  on  the  Belgian  State  Railways.  By 
M.  J.  B.  Flamme.  Inst.  Mech.  C.  E.  1905. 

Large  Locomotive  Boilers.  By  George  Churchward.  Trans.  Inst.  Mech. 
Eng.  1906. 

Ten  Years  of  Locomotive  Progress.  By  George  Montagu.  London  :  Alston 
Rivers.  1907. 

Modern  Locomotive  Practice.  A  treatise  on  the  design,  construction  and 
working  of  Steam  Locomotives.  By  C.  E.  Wolff,  B.Sc.  Manchester :  Scientific 
Publishing  Co.  1907. 

Lectures  delivered  to  the  Enginemen  and  Firemen  of  the  London  and 
South  Western  Railway  Co.  on  the  Management  of  their  Engines.  By  D. 
Drummond,  C.E.,  Chief  Mechanical  Engineer.  London  :  Waterlow  &  Sons, 
Ltd.  1907. 


INDEX 


ACCELERATION,  273 

Action  of  the  bogie,  27 
Adams'  elastic  wheel,  54 
,,       vortex  pipe,  145 
Adhesion,  55,  58 
Adjustable  blast  nozzle,  146 
Ashpans,  108 
Automatic  expansion,  255 
,,  lubricator,  283 

Axle  journals,  4 
,,     box,  5 

B. 

BACK  pressure,  138 
Balance  valves,  238 
„        weights,  79 
Bal dry's  rule,  25 
Baldwin  smoke-box,  150 
Bar  frames,  7 
Barrus  calorimeter,  164 
Belgian  locomotives,  119 
Belpaire  fire-box,  103 
Birds'  nests,  128 
Bissell  bogie,  15 
Blast  pipe,  143 
Board  of  Trade  rules,  93 
Bogie  springs,  29 
Bogies,  15 
Boiler  fittings,  180 
Boilers,  85 

Boring  cylinders,  203 
Brakes,  285 


Bridles,  237 

Buffers,  37 

Built-up  crank  axles,  211 

Bushed  small  ends,  208 

C. 

CATARACT,  229 
Centrifugal  force,  30 
Chimney,  146,  147 
Circulation,  156 
Cleaning  engines,  289 
Clinkering,  128 
Coal,  127 

Co-efficient  of  adhesion,  59 
Coke,  124 

Collision  at  Bina,  271 
Combustion,  120 
Compensating  levers,  11 

,  weights,  78 

Compounding,  239 
Connecting  rod,  204 
Constant  lead,  235 
Contact  area,  56 
Cost  of  superheaters,  262 
Counterbalancing,  73 
Coupled  wheels,  60 
Couche  and   Havrez's   experiments, 

133 
Crank  axles,  209 

,,      pin  friction,  210 
Crossed  and  open  rods,  225 
Curves,  13 
Cylinders,  202 


308 


INDEX 


D. 

DE  PAMBOUR'S  formula,  295 
Derailments,  1,  27 

„  of  tank  engines,  277,  281 

Design  of  boilers,  114 
Development  of  bar  frame,  9 
Diaphragm,  139 
Distribution  of  heat,  88,  89 
Disturbing  forces,  2 
Diverging  nozzle,  191 
Domes,  115 
Draught,  131 
Drawbar  pull,  298 
Drummond's  feed-water  heater,  269 

,,  water  tubes,  117,  118 

E. 

ELASTIC  roads,  83 
Engine  mileage,  293 
Exhaust  steam,  123 
Expansion,  217 

„          of  copper.  105 
Explosions,  89 

F. 

FAY'S  brake,  285 
Finding  centre  of  gravity,  274 
Fire  boxes,  95,  102 

„    holes,  107 
Firebrick  arch,  124 
Firing  locomotives,  129 
Flanged  steel  bogies,  19 
Flanging  press,  18 
Floating  lever,  230 
Flue  tubes,  109,  110 
Foundation  ring,  106 
Four-cylinder  engines,  246 
Frames,  1 
Friction,  209 
Front  end,  136 
Fuel,  127 

G. 

GAB  gear,  214 
Girder  slings,  105,  107 


Glass  water  gauge,  186 
Going  blind,  221 
Grate  bars,  108 
Gravity,  centre  of,  34 
Great  Eastern  Kailway  bogie,  20 
Great  Liverpool,  38 
Great  Northern  pony,  16 
»  „          bogie,  17 

Great  Western  Kailway  bogie,  21 
Guide  bars,  204 

H. 

HAMMER  blow,  79 

Heat  pegs,  154 

Heating  feed  water,  161,  265 

Horn  plates,  11 

Howe's  valve  gear,  215 

Hull  and  Barnsley  Kailway,  99 

Hydrokineter,  155 

Hyperbolic  logs,  219 

I. 

INDICATORS,  251 
Initial  condensation,  253 
Injectors,  187 
Intercepting  valves,  244 
Intermediate  receiver,  242 
Internal  disturbing  forces,  66 
Ivatt's  experiments,  257 
,,       speed  diagram,  301 

J. 
JOY'S  radial  gear,  213,  233 

K. 
KRUPP'S  disc  wheels,  44 

L. 

LA  FRANCE,  137 
Lagging,  196 
Lap,  220 
Lead,  220 
Length  of  name,  135 


INDEX 


309 


Lifting  action  of  cross  head,  71 
Lighting  up,  291 
Long  grates,  117 
Longitudinal  seams,  94 
Loss  by  radiation,  177 
Lubrication,  282 
Lurching,  87 

M. 

MARRIOTTE'S  law,  252 
Mass,  29 

Maximum  drawbar  pull,  302 
Mineral  oils,  260 


NOTKIN  superheater,  177 
Nozzle,  143 

P. 

PALLISER  bolts,  96 

Peabody  calorimeter,  165,  166 

Pet  cocks,  185 

Petticoat  pipes,  146 

Pick-up  scoops,  264 

Pielock  superheater,  177 

Pistons,  212 

Piston  valves,  246 

Plate  frames,  3 

Pop  valves,  185 

Priming,  162 

Propulsion,  66 

Purdue  University,  81 

Q. 
QUALITY  of  steam,  169 

R. 

KAMSBOTTOM  safety  valves,  184 
Range  of  temperature,  254 
Rankine's  formula,  74 
Rate  of  combustion,  130 
,,       evaporation,  132 

R.L. 


Ratio  of  expansion,  241 
Reciprocating  masses,  76 
Reversing  lever,  225 
Rolling,  71 
Running  shed,  288 


SAFETY  valves,  183 

Sanding  rails,  64 

Schenectady  No.  1,  136 

Schmidt's  superheater,  174,  175 

Screwed  stays,  95 

Self -starting  injectors,  194 

Shrinkage,  45 

Side  rods,  61,  62 

Sight  feed  lubricators,  284 

Simple  steam  engine,  199 

Slide  valves,  236 

Slipper  guide,  206,  207 

Smith's  piston  valves,  247 

Smoke-box,  137 

L.  &  S.  W.  R.,  140 
S.  E.  &  C.  R.,  141,  142 

Springs,  11 

Standard  front  end,  149 

Staybolts,  97 

Steam,  86,  152 

Steam  gas,  260 

Stephenson's  frames,  6 

,,  link  motion,  213,  223 

Stirling's  express  engine,  23 

Stresses  in  boilers,  91 

Stuffing  box,  203 

Super-elevation,  36 

Superheating,  171 

T. 

TANK  engines,  271 
Temperatures,  132 
Tenders,  263 
Testing  plant,  80 

The  locomotive  as  a  steam  engine, 
198 


310 


INDEX 


The  locomotive  as  a  steam  generator, 

84 

,,  ,,         as  a  vehicle,  1 

Theory  of  the  blast  pipe,  151 

,,         „      injector,  189 
Throttle  valves,  180,  181 
Tire  dimensions,  48,  49,  50,  51 
,,     rolling  mill,  41 
,,    sections,  46,  47,  52 
Tires,  40 

Train  resistance,  297 
Transmission  of  heat,  153 
Traversing  axle,  24 
Treatment  of  water,  159 
Tube  expanders,  111 
„     leakage,  112 


V. 

VACUUM  brake,  286 
Valve  gear,  213 


W. 

WAINWRIGHT'S  reversing  gear,  226, 

227,  228 

Walschaert's  gear,  213,  230 
Wandering,  70 
Washing  out  boilers,  291 
Wasting  of  stays,  101 
Water,  159 
Water  legs,  157 

,,      spaces,  116 
Water- tube  boilers,  170 
Wear  of  cylinders,  202 
Webb's  whirling  table,  44 
Weights  of  boilers,  113 
Westinghouse  brake,  285 
Wheel  base,  13 
Wheel  and  rail,  54 
Wheels,  40 

Wire  drawing,  255        ^^/ 
Work  of  injectors,  193 

,,        the  locomotive,  294 
Wrought  iron  wheels,  43 


UNIVERSITY 

or 
.^LIFORNV^ 


BRADBURY,   AGNEW,    &   CO.  I.D.,    PRINTERS,   LONDON  AND  TONBBIDGE. 


